Emission characteristics of Grimm-style glow discharge plasmas with helium matrix plasma gas containing small amounts of nitrogen

Glow discharge plasmas with helium–(0–16%) nitrogen mixed gas were investigated as an excitation source in optical emission spectrometry. The addition increases the sputtering rate as well as the discharge current, because nitrogen molecular ions, which act as primary ions for the cathode sputtering, are produced through Penning-type ionization collisions between helium metastables and nitrogen molecules. The intensity of a silver atomic line, Ag I 338.29 nm, is monotonically elevated along with the nitrogen partial pressure added. However, the intensities of silver ionic lines, such as Ag II 243.78 nm and Ag II 224.36 nm, gave different dependence from the intensity of the atomic line: Their intensities had maximum values at a nitrogen pressure of 30 Pa when the helium pressure and the discharge voltage were kept at 2000 Pa and 1300 V. This effect is principally because the excitations of these ionic lines are caused by collisions of the second kind with helium excited species such as helium metastables and helium ion, which are quenched through collisions with nitrogen molecules added to the helium plasma. The sputtering rate could be controlled by adding small amounts of nitrogen to the helium plasma, whereas the cathode sputtering hardly occurs in the pure helium plasma.     

Analytical performance of high-voltage neon plasma in glow discharge optical emission spectrometry

In a high-voltage Ne glow discharge plasma (Ne-GDP), calibration factors as well as the limit of determination were compared between atomic resonance lines and singly-ionized lines of copper and aluminium in optical emission spectrometry. These elements have intense ionic lines which are excited by resonance charge-transfer collisions of Ne ions. The ionic lines gave better detection sensitivity in the Ne-GDP, whereas the atomic resonance lines were commonly employed as analytical lines in the other plasma sources such as Ar-GDP and ICP. The limit of determination was 1.3 × 10^–3 mass % for the Cu II 248.58 nm line and 1.0 × 10^–3 mass % Al for the Al II 358.66 nm line at a discharge parameter of 1.60 kV/36 mA.     

Emission characteristics of Grimm-style glow discharge plasmas with helium matrix plasma gas containing small amounts of nitrogen

Glow discharge plasmas with helium–(0–16%) nitrogen mixed gas were investigated as an excitation source in optical emission spectrometry. The addition increases the sputtering rate as well as the discharge current, because nitrogen molecular ions, which act as primary ions for the cathode sputtering, are produced through Penning-type ionization collisions between helium metastables and nitrogen molecules. The intensity of a silver atomic line, Ag I 338.29 nm, is monotonically elevated along with the nitrogen partial pressure added. However, the intensities of silver ionic lines, such as Ag II 243.78 nm and Ag II 224.36 nm, gave different dependence from the intensity of the atomic line: Their intensities had maximum values at a nitrogen pressure of 30 Pa when the helium pressure and the discharge voltage were kept at 2000 Pa and 1300 V. This effect is principally because the excitations of these ionic lines are caused by collisions of the second kind with helium excited species such as helium metastables and helium ion, which are quenched through collisions with nitrogen molecules added to the helium plasma. The sputtering rate could be controlled by adding small amounts of nitrogen to the helium plasma, whereas the cathode sputtering hardly occurs in the pure helium plasma.     

Analytical performance of high-voltage neon plasma in glow discharge optical emission spectrometry

In a high-voltage Ne glow discharge plasma (Ne-GDP), calibration factors as well as the limit of determination were compared between atomic resonance lines and singly-ionized lines of copper and aluminium in optical emission spectrometry. These elements have intense ionic lines which are excited by resonance charge-transfer collisions of Ne ions. The ionic lines gave better detection sensitivity in the Ne-GDP, whereas the atomic resonance lines were commonly employed as analytical lines in the other plasma sources such as Ar-GDP and ICP. The limit of determination was 1.3 × 10^–3 mass % for the Cu II 248.58 nm line and 1.0 × 10^–3 mass % Al for the Al II 358.66 nm line at a discharge parameter of 1.60 kV/36 mA. Received: 22 January 1999 / Revised: 15 March 1999 / Accepted: 20 March 1999     

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.     

A spectral study of charge transfer and Penning processes for Cu,Zn, Ag,and Cd in a glow discharge

The occurrence of charge transfer and Penning process in glow discharge atomic emission sources can have a profound effect on the specific and overall spectral emission line characteristics of analyte species in these sources. A detailed spectral illustration of several of these effects is presented in this study for Cu, Zn, Ag and Cd with a particular focus on the ionic emission characteristics (i.e. II lines) of these elements. Charge transfer and Penning processes in glow discharge devices are driven by ionic and metastable species generated from the filler gas. Comparison of spectra obtained utilizing different filler gases is particularly effective for revealing the unique and specific excitation pathways for the analyte ions. Detailed high resolution spectra are presented and compared for Cu and Zn (brass) with Ar, Ne or He filler gases and for Ag and Cd with Ar or He as the filler gas illustrating several charge transfer and Penning processes. Unambiguous identification of spectral lines for specific transitions was facilitated by the acquisition of all spectral data utilizing a UV–visible Fourier transform spectrometer. This spectrometer provided complete and continuous coverage of the spectral region from 200 to 650 nm and allowed spectral lines to be identified with an accuracy of 1–2 pm.     

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.     

Emission Characteristics of Jet Configurations for Jet-Boosted Glow Discharge Atomic Emission Spectrometry

Comparisons of emission characteristics and analytical performance have been made between three types of jet configuration. These include cone-jet configuration, six-jet configuration, and cylinder-jet configuration. The cone-jet configuration shows the highest emission intensity among all jet configurations. Regardless of the jet configuration, the Cu II 224.70 nm emission line was found to be the most dominant of all Cu emission lines. The intensity ratios of the resonance line Cu I 324.75 to a nonresonance line Cu I 282.44 nm was 1.3 for the six-jet configuration, 2.3 for the cylinder jet, and 2.8 for the cone jet. This may indicate that self-absorption was significant in six-jet configuration. The effects of main and auxiliary gas flow rates on the emission characteristics for the cone jet configuration were also investigated. The intensity of Cu I at 324.75 and 327.40 nm decreases about 30% when the gas flow rate increased from 0 to 150 ml/min, while the intensities of Cu II 224.70 nm and the UV–Visible Cu I 510.55-, 515.32-, and 521.82-nm lines increased by a factor of 2 to 3. The decrease in intensity of the resonance line relative to the Cu II and Cu I green lines may be caused by self-absorption. The cone-jet and six-jet configurations show comparable values of precision, linearity, and detection limits, while the cylinder-jet configuration provides the worst analytical performance among three types of jet configurations. The linearity of the calibration curve was the worst in the six-jet configuration due to self-absorption.     

Classification of singly ionized iron emission lines in the 160–250 nm wavelength region from Grimm-type glow discharge plasma

In order to investigate the emission behavior of singly ionized iron lines excited by a Grimm-type glow discharge plasma, we have compiled a wavelength table of the lines in the 160–250 nm region. Three different plasma gases (argon, neon, and argon-helium mixed gas) have been employed to compare the relative intensities of the ionic iron lines. It is found that the emission intensities of some line groups which appear in the wavelength range of less than 190 nm are especially dependent on the nature of the plasma gas employed. These excitations can be principally explained from charge transfer collisions between iron atoms and plasma gas ions.     

Comparison in the analytical performance between krypton and argon glow discharge plasmas as the excitation source for atomic emission spectrometry

The emission characteristics of ionic lines of nickel, cobalt, and vanadium were investigated when argon or krypton was employed as the plasma gas in glow discharge optical emission spectrometry. A dc Grimm-style lamp was employed as the excitation source. Detection limits of the ionic lines in each iron-matrix alloy sample were compared between the krypton and the argon plasmas. Particular intense ionic lines were observed in the emission spectra as a function of the discharge gas (krypton or argon), such as the Co II 258.033 nm for krypton and the Co II 231.707 nm for argon. The explanation for this is that collisions with the plasma gases dominantly populate particular excited levels of cobalt ion, which can receive the internal energy from each gas ion selectively, for example, the 3d⁷4p ³G₅ (6.0201 eV) for krypton and the 3d⁷4p ³G₄ (8.0779 eV) for argon. In the determination of nickel as well as cobalt in iron-matrix samples, more sensitive ionic lines could be found in the krypton plasma rather than the argon plasma. Detection limits in the krypton plasma were 0.0039 mass% Ni for the Ni II 230.299-nm line and 0.002 mass% Co for the Co II 258.033-nm line. However, in the determination of vanadium, the argon plasma had better analytical performance, giving a detection limit of 0.0023 mass% V for the V II 309.310-nm line.     

Comparative studies on excitation of nickel ionic lines between argon and krypton glow discharge plasmas

The emission characteristics of nickel ionic lines in a glow discharge plasma are investigated when argon or krypton was employed as the plasma gas. Large difference in the relative intensities of nickel ionic lines which are assigned to the 3d⁸4p–3d⁸4s transition is observed between the krypton plasma and the argon plasma. Different intense Ni II lines appear in the krypton spectrum and in the argon spectrum, such as the Ni II 231.601 nm for Kr and the Ni II 230.009 nm for Ar. The excitation energy of these Ni II emission lines can give a key in considering their excitation mechanisms. The explanation for these experimental results is that charge-transfer collisions between nickel atom and the plasma gas ion play a major role in exciting the 3d⁸4p excited levels of nickel ion. The conditions for energy resonance in the charge-transfer collision determine particular energy levels having much larger population; for example, the 3d⁸4p ⁴D_7/2 level (6.39 eV) for Kr and the 3d⁸4p ⁴P_5/2 level (8.25 eV) for Ar.     

Two-dimensional observation of emission spectra excited from laser induced plasmas and the application to emission spectrometric analysis.

The spatial distribution analysis of emission signals from a laser-induced plasma can provide information on the excitation mechanism as well as on the optimization of the analytical conditions when it is employed as a sampling and excitation source in optical emission spectrometry. A two-dimensionally imaging spectrometer system was employed to measure spatial variations in the emission intensities of a copper sample and plasma gases when krypton, argon, or helium was employed under various pressure conditions. The emission image of the Cu I 324.75-nm line consists of a breakdown spot and a plasma plume, where the breakdown zone expands toward the surrounding gas. The shape and the intensities of the plasma plume are strongly dependent on the kind and pressure of the plasma gas, while those of the breakdown zone are less influenced by these experimental parameters. This effect can be explained by the difference in the cross-section of collisions between krypton, argon, and helium. The signal-to-background ratio of the Cu I 324.75-nm line was estimated over two-dimensional images to determine the optimum position for analytical applications.     

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.     

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.     

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     

Direct determination of arsenic in steel by glow discharge optical emission spectrometry with argon-helium mixed gas.

In glow discharge optical emission spectrometry, an argon-helium mixed gas plasma was investigated to improve the detection sensitivity of arsenic in steel samples. The emission line of arsenic was enhanced and the background intensity was simultaneously reduced when an Ar-He plasma was employed instead of an Ar plasma, which is effective for the sensitive determination of arsenic. The detection limits were calculated to be 0.009 mass% for a 700-V Ar plasma, 0.004 mass% for a 700-V Ar-He plasma, and 0.001 mass% for a 900-V Ar-He plasma.     

Collisional–radiative model for the sputtered copper atoms and ions in a direct current argon glow discharge

A collisional–radiative model is developed for various levels of the sputtered copper (Cu) atoms and their ions in an argon (Ar) direct current glow discharge, used as an analytical source for optical emission spectrometry. In this application, attention is paid to the photons emitted by sputtered atoms and ions, and hence to the behavior of excited levels of these species. 8 Cu atomic and 7 Cu⁺ ionic levels are considered in the model, as well as the Cu²⁺ ions. Typical results of the model are the level populations (in two dimensions) of the various levels, and the relative contributions of the different populating and depopulating processes. This model is not only of interest for analytical glow discharge optical emission spectrometry, but also for plasma diagnostic tools and for copper–vapor lasers.     

Furnace atomization plasma emission spectrometry with He/Ar mixed gas plasmas

The influence of plasma gas composition on the operating and analytical characteristics of a furnace atomization plasma emission source (FAPES) is presented. He I and Ar I excitation temperatures increase 30% in the mixed gas plasmas whereas argon ion excitation temperatures decrease from 33 000 K to 26 000 K in the presence of He. Collisional exchange of internal energy between excited states of Ar and He accounts for these changes. Average analyte ionization temperatures (for Cr, Mn, Mg, Co, Fe, Cd and Zn), derived from the relative emission intensities of their ionic and atomic lines in a 40-MHz 50-W plasma, increase from 5270 K to 6740 K with the addition of Ar to He. Ionic line intensities increase from 10-fold (Mn) to 40-fold (Cd, Zn) with addition of Ar to the plasma while atomic line intensities increase only twofold. Limits of detection remain substantially unaltered for atomic transitions due to increased noise but are improved twofold (Cd) to 24-fold (Mn) for ionic transitions. The analytical advantages and disadvantages of mixed gas plasmas are discussed. The Ne I excitation temperature at 40 MHz and 50 W was determined to be 4330±80 K.     

Factors affecting the formation of the radiation pre-peak at the operation of a Grimm-type source in pulsed DC mode

The plasma emission pre-peaks of many atomic and ionic spectral lines of Cu and Ar were systematically investigated in a Grimm-type pulsed glow discharge (PGD). To register the pre-peaks with sufficient time resolution, a monochromator with photomultiplier detection was used. When the applied power exceeded a specific threshold, pre-peaks were found in all spectral lines investigated, and it was revealed that the electrical pre-peak was the cause of the atomic emission pre-peak. The form and intensity of the pre-peak radiation were, however, found to be different for different atomic emission lines. The excitation energy of the upper energy level of the atomic line transition, and factors related to recombination and self-absorption, were found to affect the emission pre-peak. Pre-peaks observed when using pulsed DC and pulsed radio-frequency power were compared. This investigation provides insight into best practice when selecting spectral lines most suitable for analytical spectrometry using PGD.