Ar Emission Lines Research Articles

Optical emission spectroscopy of an industrial thermal atmospheric pressure plasma jet: Parametric study of electron temperature

The plasma parameters of an industrial atmospheric pressure plasma jet (APPJ) are measured as a function of the electric power of the plasma generator, the gas flow, and the distance from the jet nozzle exit. The APPJ device operates an electric discharge under Argon gas flow resulting into a continuous Argon plasma jet in the kW power range expanding into ambient air. The plasma temperature Te and electron number density Ne are determined by optical emission spectroscopy (OES) analyzing up to 17 emission lines of neutral Ar (I) and singly-ionized Ar (II) species using the Saha-Boltzmann plot (SBP) method. For the accurate determination of plasma parameters a methodology is developed to overcome fundamental limitations in OES of Argon plasma that is due to the strongly different intensities of Ar (I) and Ar (II) emission lines. The most significant step is the use of spectral bandpass filters in the optical collection system. The experimental parameters of the jet device are playing a crucial role for APPJ applications (e.g. thermal load to the workpiece, plasma chemistry interaction etc.). We measure Te and Ne in dependence of the experimental parameters and obtain consistent and accurate values of Te = 9000 ± 150 K and Ne = 5 × 1015 cm−3 (typ.). For comparison, plasma characterization using only the neutral Ar lines gives inaccurate and inconsistent Te values. This highlights the importance of using also the ionic Ar lines. The developed methodology may be diversified and applied also for OES of other rare gas plasma.

Spectral study of the Galactic ridge X-ray emission with Suzaku: Comparison of the spectral shape with point sources

Abstract The Galactic ridge X-ray emission (GRXE) is unresolved X-ray emission located on the Galactic plane, and whether the GRXE comes from truly diffuse plasma or unresolved point sources is still debatable. We present results of spectral analysis of the GRXE with Suzaku. In order to examine the point source origin, we fitted the GRXE spectra in the 1.2–10 keV energy band with a point source model, which is a mixture of active binary stars (ABs) and non-magnetic cataclysmic variables (non-mCVs), and found that the model cannot represent the GRXE spectral shape as long as the standard metal abundances of these species are assumed. In particular, the standard abundance model cannot account for the observed intensities of Si, S, and Ar lines as well as the previously reported Fe line. Assuming spatial densities in the solar neighborhood, integration of the ABs and non-mCVs accounts for only 30% of the observed GRXE flux. Other species of the point sources or diffuse emission with stronger Si, S, Ar, and Fe emission lines shall explain the rest.

Emirates Mars Ultraviolet Spectrometer's (EMUS) Observation of Argon in the Martian Thermosphere

AbstractThe Emirates Mars Ultraviolet Spectrometer (EMUS) is a far ultraviolet spectrometer on‐board the Emirates Mars Mission's (EMM) which arrived at Mars on 9 February 2021. EMUS is designed to observe key neutral species in the Martian thermosphere (100–200 km) and exosphere (≥200 km). EMUS has observed two neutral argon (Ar) emission lines, Ar I 104.8 nm and Ar I 106.6 nm, in the thermosphere. Our interest in these emissions stem from argon's non‐reactiveness, making it a tracer for transport between the upper and lower atmosphere. We report average argon disk brightness measured by EMUS and compare them to measurements from Earth orbiting observatories. For the first time, this work investigates the variability of Ar I 106.6 nm brightness due to emission angles, solar zenith angles, solar longitudes, local times and latitudes. To contrast the behavior of inert argon we compare these results with the photochemically reactive oxygen 135.6 nm.

Feasibility of two-dimensional die-level plasma process monitoring using spatially resolvable optical emission spectrometers

We demonstrated the feasibility of die-level process monitoring using spatially resolvable optical emission spectrometers (SROESs) in a low-pressure plasma reactor. The spatially resolved Ar emission line intensities and their intensity ratios were obtained from uniformly generated and intentionally perturbed plasma by inserting conductors of known sizes at known locations. The sheath and perturbed plasma distributions were identified from the Ar emission line intensity and their intensity ratio in the lateral direction to the SROES installment orientation. However, the resolution in the axial direction was insufficient to identify the sheath and perturbed the plasma distribution. We propose the superimposition of measured plasma emission intensities from two perpendicularly aligned SROESs for die-level process monitoring. The insufficient axial resolution can be compensated for by the lateral resolution of another SROES, and die-level process monitoring using SROES can thus be realized.

On the rotational–translational equilibrium in non-thermal argon plasmas at atmospheric pressure

This work examines the rotational–translational equilibrium in non-thermal, argon-based plasmas at atmospheric pressure. In particular, rotational temperatures (T rot) and neutral gas temperatures (T g) are compared along the axis of plasma columns sustained by either radiofrequency (RF) or microwave (MW) electromagnetic fields. Water vapours or N2 admixtures are added to the high-purity argon plasmas to record the rotational temperatures from the emission spectra of either the OH(A2Σ + − X2Π i ) or the N2 +(B2Σ u + − X2Σ g + ) rovibrational systems. T g values are also deduced from the line broadening of selected Ar emission lines using an hyperfine spectrometer. In the MW Ar/H2O plasma, T g decreases from ∼2100 K close to the wave launcher to ∼1600 K near the end of the plasma column, while T rot is mostly constant in the 1500 K range. In presence of N2 admixtures instead of water vapours, T g is higher by about 300 K (from ∼2400 K to ∼1900 K), while T rot decreases from ∼3200 K to ∼2750 K along the plasma column. A discrepancy between T g and T rot is also observed in the much colder RF plasmas with T g ∼ 400 K and T rot ∼ 515 K. Such departure from the rotational–translational equilibrium in both plasmas is ascribed to the influence of electrons competing with neutrals to impose their own temperature on the distribution of rotational levels of both ground and excited states.

Calibration of Raman wavenumber in large Raman images using a mercury‐argon lamp

AbstractRaman imaging is an emerging tool for the analysis of meteorites, as it is capable of describing mineralogy, carbon composition/speciation, and crystal orientation all within a petrographic context. Adequately examining the heterogeneous composition of a meteorite often requires long image collection times on the timescale of days. However, the wavenumber calibration of the Raman spectrometer drifts over long timescales resulting in low wavenumber precision for the Raman spectra comprising a large Raman image. This decrease in wavenumber precision can compromise the analysis of geological markers that can provide important information on a meteorite sample. We examine, in detail, the change in bandwidth and wavenumber of the Raman bands and Hg–Ar emission lines in our Raman images as a function of time and laboratory temperature. To overcome the drift in calibration, we utilize a commercial WITec Raman instrument with a built‐in Hg–Ar calibration lamp to individually calibrate each spectrum in the Raman image. We show that using the Hg–Ar calibration, we can improve the wavenumber precision for the spectra in our Raman images from ~±0.15 to ~±0.05 cm−1 for Raman spectra collected over multiple days. This is important as it improves measurements of mineral chemistry, latent strain, and other features that are dependent upon accurate peak position determination. We also examine the spectral signal‐to‐noise ratio needed to minimize the wavenumber error when fitting bands to Gaussian/Lorentzian profiles. We then use our results to suggest a general method for calibrating the wavenumber of Raman spectra in large Raman images.

Comparative studies of compact kHz and MHz driven low pressure plasmas by emission and laser spectroscopy

The temporal evolution of a low pressure argon plasma driven by a combination of radio frequency and kilohertz frequency power sources was characterized by phase resolved optical emission and laser absorption spectroscopy. The compact, low pressure plasma was formed in a hybrid surface/jet geometry and powered by a high voltage power supply operating at 31 kHz and by a lower voltage RF supply operating at 13.56 MHz. An accurate evaluation of the 1s state density dynamics was performed by means of laser absorption measurements of the 1s5 and 1s4 sublevels. The emission spectra were recorded with a submicrosecond temporal resolution and evaluated using an extended Corona model. In comparison with the modeling results, the phase dependent ratio of different Ar(2p) → Ar(1s) emission lines was used to determine temporal profiles of electron temperature and relative electron density. The results were compared with the results from time averaged emission measurements by performing an identical analysis. Strong spatial and temporal variations of plasma parameters were observed when the plasma was driven solely by the 31 kHz source, resulting in nonequilibrium conditions for long living states. Inconsistent observations in the reconstructed temporal development of plasma energy and density were further investigated by illustrating full spatiotemporal reconstruction of plasma parameters. These results permit clear identification of strong spatial gradients through the tube.

Determination of Arsenic by Hydride Generation—Laser-Induced Breakdown Spectroscopy: Characterization of Interelement Interferences

ABSTRACTIn this study, interelement interferences were evaluated for the determination of arsenic in aqueous samples through laser-induced breakdown spectroscopy (LIBS) hyphenated with a hydride generation sample introduction system. Optimum instrumental and chemical parameters were selected and variation in LIBS signal intensity was recorded for As solution in the presence of comparable concentrations of interfering elements. No significant change in the signal intensity of As(I) 228.8 nm line was observed in the presence of alkali/alkali earth metals; however, the presence of hydride-forming elements has shown a noticeable decrease in the line emission strength of arsenic. The least variation in arsenic signal was observed in the presence of Ge, the most volatile of all. However, the signal has decreased to a greater extent in the presence of Sn, Sb, and Pb. The presence of interfering elements on electron temperature and electron number density of arsenic plasma has also been studied. Plasma temperatures calculated using both As and Ar emission lines in the Boltzmann equation were similar, being around 5000 K. The McWhirter criterion for stationary and homogenous plasmas was utilized for the establishment of the local thermodynamic equilibrium under the plasma conditions studied. Applicability of the technique for multielemental analysis of water samples was tested through spiking experiments. Arsenic signal showed 26% decrease in the multielemental mixture solution. LIBS is among a few atomic spectroscopic techniques that facilitate rapid and simultaneous multielemental analysis without extensive sample preparation steps. However, the analytical performance of the technique still requires more serious efforts to compete with other conventional techniques for routine analysis of environmental samples.

Cleaning level of the target before deposition by reactive direct current magnetron sputtering

We present a thorough study of the target-cleaning phase to estimate the healthiness of the target in a direct current (DC) magnetron sputtering deposition. The study is based on real-time plasma monitoring by means of optical emission spectroscopy during a traditional cleaning phase in an Ar atmosphere. In this work we demonstrate that intensities of Ar emission lines are sufficient indicators of the target cleanliness degree. To derive these results SiOxNy thin films were grown by reactive DC magnetron sputtering on silicon wafers for different deposition configurations of Ar, O2 and N2 fluxes. Refractive index of the resulting films is measured by in-situ spectroscopic-ellipsometry. A simple but robust estimator is used to determine the time when the target is ready to start deposition. Hence, this approach can be suited for an industrial environment since the time invested in the cleaning phase can be minimized avoiding the waste of material and time.

Ground state atomic oxygen in high-power impulse magnetron sputtering: a quantitative study

The ground state density of oxygen atoms in reactive high-power impulse magnetron sputtering discharges has been studied quantitatively. Both time-resolved and space-resolved measurements were conducted. The measurements were performed using two-photon absorption laser-induced fluorescence (TALIF), and calibrated by optical emission actinometry with multiple Ar emission lines. The results clarify the dynamics of the O ground state atoms in the discharge afterglow significantly, including their propagation and fast decay after the plasma pulse, as well as the influence of gas pressure, O2 admixture, etc.

Study of Ar and Ar-CO2 microwave surfaguide discharges by optical spectroscopy

A surfaguide microwave discharge operating at 2.45 GHz in Ar and Ar-CO2 mixtures is studied using diagnostics methods based on optical emission spectroscopy. The population densities of Ar metastable and resonant states of the lowest group of excited levels (1sx) are investigated for several experimental conditions using the self-absorption technique. It is found that the densities of these levels, ranging from 1017 to 1016 m−3 for the pure Ar case, are dependent on the discharge pressure and applied power. The electron temperature and electron density are calculated via the balances of creation/loss mechanisms of radiative and metastable levels. In the range of the studied experimental conditions (50–300 W of applied power and 0.5–6 Torr of gas pressure), the results have shown that lower values of electron temperature correspond to higher values of power and pressure in the discharge. Adding CO2 to the argon plasma results in a considerable decrease (about 3 orders of magnitude) of the Ar metastable atom density. The feasibility of using the ratio of two Ar emission line intensities to measure the electron temperature in CO2 discharges with small Ar admixtures is studied.

Detection of fast electrons in pulsed argon inductively-coupled plasmas using the 420.1–419.8 nm emission line pair

Pulsed rf plasmas exhibit many differences as compared to continuous wave plasmas with the same average power levels, including large temporal variations in the electron temperature, with a sharp spike when the power is applied and falling dramatically in the afterglow. We present a comparison of time-resolved measurements of the effective electron temperature in pulsed inductively-coupled plasmas by means of (i) optical emission spectroscopy (OES) using different sets of argon emission lines and (ii) Langmuir probe measurements. One OES diagnostic used six strong Ar() emission lines in the 700–800 nm wavelength range, the second used only the Ar 420.1–419.8 nm line pair. For pulsed plasmas with long afterglow periods, the line pair method reveals the presence of a significant number of hot electrons ( eV) at the start of the pulse. Under these conditions, the metastable atom density is very low, and the diagnostic using the Ar() emission lines is ineffective for determining the electron temperature. For later parts of the pulse and pulsed plasmas with short periods (i.e. 10 μs), the metastable density is high and the two OES methods yield similar results which are also in agreement with probe measurements.

An atmospheric-pressure, high-aspect-ratio, cold micro-plasma.

An atmospheric pressure nonequilibrium Ar micro-plasma generated inside a micro-tube with plasma radius of 3 μm and length of 2.7 cm is reported. The electron density of the plasma plume estimated from the broadening of the Ar emission line reaches as high as 3 × 1016 cm−3. The electron temperature obtained from CR model is 1.5 ev while the gas temperature of the plasma estimated from the N2 rotational spectrum is close to room temperature. The sheath thickness of the plasma could be close to the radius of the plasma. The ignition voltages of the plasma increase one order when the radius of the dielectric tube is decreased from 1 mm to 3 μm.

Combined optical emission and resonant absorption diagnostics of an Ar-O2-Ce-reactive magnetron sputtering discharge

We report the results on combined optical characterization of Ar-O2-Ce magnetron sputtering discharges by optical emission and resonant absorption spectroscopy. In this study, a DC magnetron sputtering system equipped with a movable planar magnetron source with a Ce target is used. The intensities of Ar, O, and Ce emission lines, as well as the absolute densities of Ar metastable and Ce ground state atoms are analyzed as a function of the distance from the magnetron target, applied DC power, O2 content, etc. The absolute number density of the Arm is found to decrease exponentially as a function of the target-to-substrate distance. The rate of this decrease is dependent on the sputtering regime, which should be due to the different collisional quenching rates of Arm by O2 molecules at different oxygen contents. Quantitatively, the absolute number density of Arm is found to be equal to ≈3×108cm−3 in the metallic, and ≈5×107cm−3 in the oxidized regime of sputtering, whereas Ce ground state densities at the similar conditions are found to be few times lower. The absolute densities of species are consistent with the corresponding deposition rates, which decrease sharply during the transition from metallic to poisoned sputtering regime.

Optimization of the operating conditions of solid sampling electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry for the sensitive direct analysis of powdered rice

Two different approaches were used to improve the capabilities of solid sampling (SS) electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) for the direct analysis of powdered rice. Firstly, a cooling step immediately before and after the vaporization step in the ETV temperature program resulted in a much sharper analyte signal peak. Secondly, point-by-point internal standardization with an Ar emission line significantly improved the linearity of calibration curves obtained with an increasing amount of rice flour certified reference material (CRM). Under the optimized conditions, detection limits ranged from 0.01 to 6ngg−1 in the solid, depending on the element and wavelength selected. The method was validated through the quantitative analysis of corn bran and wheat flour CRMs. Application of the method to the multi-elemental analysis of 4-mg aliquots of real organic long grain rice (white and brown) also gave results for Al, As, Co, Cu, Fe, Mg, Se, Pb and Zn in agreement with those obtained by inductively coupled plasma mass spectrometry following acid digestion of 0.2-g aliquots. As the analysis takes roughly 5min per sample (2.5min for grinding, 0.5–1min for weighing a 4-mg aliquot and 87s for the ETV program), this approach shows great promise for fast screening of food samples.

Direct analysis of soils by ETV-ICP-AES: a powerful tool for mineral exploration

A fast method for the direct analysis of soils, namely solid sampling (SS) electrothermal vapourization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES), was validated through the accurate analysis of a soil standard reference material (SRM) using another soil SRM as a calibration standard and an Ar emission line as internal standard to compensate for sample loading effects on the plasma. Good agreement was obtained between the measured concentrations and certified values according to a Student’s t-test. The validated method was applied to the determination of the distribution of elements in depth profile soil samples from across the Talbot Lake VMS Cu-Zn prospect, in the Flin Flon-Snow Lake terrane, Manitoba, Canada. These profiles revealed that: Zn, P and Ag had anomalously high concentrations at 20–50 cm depth at 400 m, above where the easternmost part of the ore deposit is located along a 0–1000 m sampling line; Cu, Al, Ba, Pb and Hg were concentrated on the surface and at 40-cm depth mostly between 500 and 600 m; and Cl, Br and I were concentrated at depth at 400 m and over all depths at 600 m. As the geochemical anomaly is known to lie from 400 to 600 m, all these elements could be used to locate the ore. Good agreement was obtained with results by ICP mass spectrometry (ICP-MS) following aqua regia (AR) digestion, for those elements that could be determined by ICP-MS. In fact, not only is sample dissolution unnecessary but qualitative analysis by SS-ETV-ICP-AES is sufficient to obtain depth profiles, including for elements like Cl, which cannot be determined when AR is used for digestion.

Improvement of the capabilities of solid sampling ETV-ICP-OES by coupling ETV to a nebulisation/pre-evaporation system

The outlet of a solid sampling (SS) electrothermal vaporization (ETV) system was coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) through a switching tee, which was itself connected to the side arm of a sheathing device inserted between a nebulizer/spray chamber system and the ICP torch. The valve was used to evacuate the pyrolysis products during the ashing step and to direct analytes towards the ICP during the vaporisation step, so that they would merge with a pre-evaporated aerosol. The aerosol exiting the spray chamber was indeed heated by infrared heating of the sheathing device and bottom of the torch to 400 °C. This system allowed the introduction of more than twice the amount of solid sample (i.e. 13 mg instead of 5 mg) without extinguishing the plasma, as only the analyte portion actually reached the ICP. Under optimum conditions and compared to conventional SS-ETV-ICP-OES (where the ETV outlet is directly connected to the torch), improvement in sensitivity by up to 5-fold and detection limit by up to 20-fold was obtained for a range of elements, the improvement being in general larger for ionic emission lines than for atomic ones. This system also allowed an accurate but more precise (by about 2-fold on average) analysis of a soil certified reference material (CRM) using another soil CRM for external calibration and an Ar emission line for internal standardization than conventional SS-ETV-ICP-OES.

INTERSTELLAR AND EJECTA DUST IN THE CAS A SUPERNOVA REMNANT

Infrared continuum observations provide a means of investigating the physical composition of the dust in the ejecta and swept up medium of the Cas A supernova remnant. Using low resolution Spitzer IRS spectra (5-35 $\mu$m), and broad-band Herschel PACS imaging (70, 100, and 160 $\mu$m), we identify characteristic dust spectra, associated with ejecta layers that underwent distinct nuclear burning histories. The most luminous spectrum exhibits strong emission features at $\sim9$ and 21 $\mu$m and is closely associated with ejecta knots with strong Ar emission lines. The dust features can be reproduced by magnesium silicate grains with relatively low Mg to Si ratios. Another dust spectrum is associated with ejecta having strong Ne emission lines. It has no indication of any silicate features, and is best fit by Al$_2$O$_3$ dust. A third characteristic dust spectrum shows features that are best matched by magnesium silicates with a relatively high Mg to Si ratio. This dust is primarily associated with the X-ray emitting shocked ejecta, but it is also evident in regions where shocked interstellar or circumstellar material is expected. However, the identification of dust composition is not unique, and each spectrum includes an additional featureless dust component of unknown composition. Colder dust of indeterminate composition is associated with emission from the interior of the SNR, where the reverse shock has not yet swept up and heated the ejecta. Most of the dust mass in Cas A is associated with this unidentified cold component, which is $\lesssim0.1$ $M_{\odot}$. The mass of warmer dust is only $\sim 0.04$ $M_{\odot}$.

Ethnic background and gender identification using electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry for forensic analysis of human hair

Multi-elemental analysis of human hair was performed by solid sampling (SS) electrothermal vaporisation (ETV) inductively coupled plasma optical emission spectrometry (ICP-OES) and multivariate analysis then carried out to discriminate general ethnicity and gender. This approach is advantageous over digestion and nebulisation, as it eliminates possible contamination or analyte loss that can occur during digestion, requires a smaller sample mass for analysis, and eliminates the dilution that follows digestion. Hair samples were first washed with water and hexane, and then dried before being ground up. Thirteen samples from different people with various ethnic backgrounds were analysed. Aliquots (of 4 mg) were placed in graphite boats that were then introduced in the ETV furnace using an autosampler. No quantification of the elements in hair was necessary. Point-by-point internal standardization with an Ar emission line was systematically carried out to compensate for sample loading effects on the plasma. Then, peak area was integrated and divided by the actual sample mass before being used in combination with multivariate analysis. Elements showing the highest loadings with principal component analysis (PCA) were considered for linear discriminant analysis (LDA). One group of elements, Li, Mo, S, Sr, Cr, K, Ni, Zn and Pb correctly identified all 13 samples for general ethnicity with LDA, whereas this was not possible with PCA. On the other hand, both PCA and LDA correctly assigned all samples for gender using Mg, S, Sr and Zn. The larger number of elements (9 for general ethnicity versus 4 for gender) is commensurate with the greater variety of ethnicities. The technique was also successfully applied to two blind samples from people living in cities as far as 430 km away from where the samples used for the training set were collected. Clearly, SS-ETV-ICP-OES in combination with LDA shows great potential as a tool for forensic analysis of hair.

Advantages and effects of nitrogen doping into the central channel of plasma in axially viewed-inductively coupled plasma optical emission spectrometry

The effects and benefits of N2 addition to the central channel of the ICP through the nebulizer gas used in ICP OES with axial view configuration were investigated in the present study. The N2 flow rate, nebulizer gas flow rate, RF power and sample uptake rate were evaluated and compared for two sample introduction systems (pneumatic nebulization/aerosol desolvation and conventional pneumatic nebulization). It was observed that N2 did not affect solution nebulization and aerosol transport but affects the ICP characteristics. The higher thermal conductivity of N2 (in comparison with Ar) changes energy distribution in the ICP, observed by monitoring the signals of Ar emission lines and sodium emission. The ratio Mg(II)-280.270nm/Mg(I)-285.213nm was utilized as a diagnostic tool for plasma robustness. The addition of N2 (20mLmin−1) increased plasma robustness significantly and mitigated effects caused by Na, K and Ca. For 40 spectral lines evaluated, it was observed that the emission signals of ionic spectral lines were in general more affected by N2 than those of atomic spectral lines. Detection limits, precision, sensitivity and linearity of calibration curves obtained using N2-Ar-ICP were almost similar to those obtained using Ar-ICP. The analysis of 5 different reference materials revealed that accuracy was not degraded by adding N2 to the Ar-ICP.