Argon Emission Research Articles

Miniature microwave plasma antenna at 2.45 GHz

New unique miniature plasma antenna driven by a one microwave signal at frequency of 2.45 GHz is constructed and tested. The length of the antenna (l = 16 mm) is much shorter than the free space wavelength of the signal. The parameters of the plasma column (n = 2.6±0.4×10 18 m -3 , T e = 3.1±0.2 eV) are obtained from argon emission spectrum by applying the line ratio method. The simulations of this monopole antenna reveal that in the standing wave regime the plasma antenna is effective transmitter at a frequency of 2.45 GHz. The results we obtained show that the shape of the radiation pattern of the plasma antenna depends on the plasma density, the exciter and the distance above the grounded plane.

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.

Atmospheric pressure argon surface discharges propagated in long tubes: physical characterization and application to bio-decontamination

Pulsed corona discharges propagated in argon (or in argon with added water vapor) at atmospheric pressure on the interior surface of a 49 cm long quartz tube were investigated for the application of surface bio-decontamination. H2O molecule dissociation in the argon plasma generated reactive species (i.e. OH in ground and excited states) and UV emission, which both directly affected bacterial cells. In order to facilitate the evaluation of the contribution of UV radiation, a DNA damage repair defective bacterial strain, Escherichia coli DH-1, was used. Discharge characteristics, including propagation velocity and plasma temperature, were measured. Up to ~5.5 and ~5 log10 reductions were observed for E. coli DH-1 bacteria (from 106 initial load) exposed 2 cm and 44 cm away from the charged electrode, respectively, for a 20 min plasma treatment. The factors contributing to the observed bactericidal effect include desiccation, reactive oxygen species (OH) plus H2O2 accumulation in the liquid phase, and UV-B (and possibly VUV) emission in dry argon. The steady state temperature measured on the quartz tube wall did not exceeded 29 °C; the contribution of heating, along with that of H2O2 accumulation, was estimated to be low. The effect of UV-B emission alone or in combination with the other stress factors of the plasma process was examined for different operating conditions.

Optical emission spectroscopy of glow, Townsend-like and radiofrequency DBDs in an Ar/NH3 mixture

Three homogeneous DBD modes have been observed in argon ammonia Penning mixture. The transition from glow to Townsend-like to radiofrequency modes happens when the frequency increases from 50 kHz and 9.6 MHz. The aim of this paper is to characterize these modes based on the study of optical emission spectra. The transition from glow mode to Townsend-like mode is characterized by stronger argon emissions associated to higher energetic electrons. The radio-frequency mode is characterized by a continuum in the UV–vis range. This continuum is attributed to bremsstrahlung emission. Its presence is explained by a high density of less energetic electrons which is consistent with a decrease of argon emissions and an increase of the NH 336 nm system associated with electrons of low energy.

Contribution of multiple electron trajectories to high-harmonic generation in the few-cycle regime

We use a few-cycle, carrier-envelope-phase (CEP) stabilized laser system to generate high-harmonic emission in argon, neon, and carbon dioxide. The high-harmonic spectra consist of discrete harmonic orders whose positions shift as a function of the CEP. Near the cutoff harmonic, the peaks are separated by two photon orders, and can correspond to either even or odd harmonics of the driving laser frequency, depending on the value of the CEP. In the plateau region, harmonic orders are separated by only one photon order. We develop a simple model which predicts the observed behavior. We use the observed dependence of the harmonic peaks as a function of CEP as a method to measure the statistical CEP fluctuations of the laser system. The measured rms fluctuation of 0.17 radians agrees with optical measurements. The high-harmonic approach to measuring CEP stability has the advantage that it is less sensitive to laser intensity fluctuations than are optical methods.

Electron heating and density production in microwave-assisted helicon plasmas

Microwaves are injected into argon and helium helicon plasmas at 6 to 20 mTorr neutral pressure, 1.2 kW pulsed microwave power, up to 500 W continuous RF power, and up to 1 kG magnetic fields, with the objective of heating the tail of the electron energy distribution function (EEDF) and populating ion metastable states. Langmuir probes are used to measure the EEDF and optical emission spectroscopy is used to monitor ion emission. The injection of microwave power in argon helicon plasmas is shown to heat the high energy tail of the EEDF without increasing the plasma density. Argon ion emission is shown to increase by a factor of 4. Injection of microwaves into a helium helicon plasma is shown to cool the bulk of the of the EEDF and increase the plasma density. Previously absent helium ion emission lines are observed with the injection of microwaves. All the microwave results are shown to be independent of RF power within the limits of the system.

Correlating metastable-atom density, reduced electric field, and electron energy distribution in the post-transient stage of a 1-Torr argon discharge

Temporal measurement of electron density, metastable-atom density, and reduced electric field are used to infer the dynamic behavior of the excitation rates describing electron-atom collision-induced excitation in the positive column of a 1 Torr argon plasma by invoking plausible assumptions regarding the shape of the electron energy distribution function performed in Adams et al (2012 Phys. Plasmas 19 023510). These inferred rates are used to predict the 420.1 nm to 419.8 nm argon emission ratio, which agree with experimental results when the assumptions are applicable. Thus the observed emission ratio is demonstrated to be dependent on the metastable-atom density, electron density, and reduced electric field. The established confidence in the validity of this emission-line-ratio model allows us to predict metastable argon-atom density during the post-transient phase of the pulse as suggested by De Joseph et al (2005 Phys. Rev. E 72 036410). Similar inferences of electron density and reduced electric field based on readily available diagnostic signatures may also be afforded by this model.

Spectroscopic Studies of Magnetron Sputtering Plasma Discharge in Cu/O2/Ar Mixture for Copper Oxide Thin Film Fabrication

Magnetron sputtering plasma for the deposition of copper oxide thin film has been investigated using optical emission spectroscopy and Langmuir probe. The intensity of the light emission from atoms and radicals in the plasma were measured using optical emission spectroscopy (OES). Then, Langmuir probe was employed to estimate the plasma density, electron temperature and ion flux. In present studies, reactive copper sputtering plasmas were produced at different oxygen flow rate of 0, 4, 8 and 16 sccm. The size of copper target was 3 inches. The dissipation rf power, Ar flow rate and working pressure were fixed at 400 W, 50 sccm and 22.5 mTorr, respectively. Since the substrate bias plays an important role to the thin film formation, the substrate bias voltages of 0, -40, -60 and -100 V were studied. Based on OES results, oxygen emission increased drastically when the oxygen flow rate above 8 sccm. On the other hand, copper and argon emission decreased gradually. In addition, Langmuir probe results showed a different ion flux when substrate bias voltage was applied. Based on these plasma diagnostic results, it has been concluded that the optimized parameter to produce copper oxide thin film are between -40 to -60 V of substrate bias voltage and between 8 to 12 sccm of oxygen flow rate.

Interpretation of the optical emission of argon in the plume of the Advanced Plasma Source

The plume of the argon plasma of the Advanced Plasma Source employed for the deposition of optical coatings has been investigated by means of optical emission spectroscopy, Langmuir probe measurements as well as collisional radiative modeling using the measured electron energy probability function as the input. The emission of the ten argon lines considered is found to exhibit a cone-shaped spatial distribution. The emission on the axis of symmetry decreases exponentially with increasing distance from the source in good agreement with the results obtained by collisional radiative modeling and the radial extension of the Gaussian profile in the radial direction increases linearly along the axial direction. The analysis of the measured electron properties shows in particular that the electron pressure varies between about 2 Pa near the plasma source exit and 1 mPa at larger distances. The argon neutral density determined by collisional radiative modeling is found to be about 6 · 1011 cm−3 in the plasma plume in front of the source exit corresponding to a degree of ionization as high as 60%.

MID-IR SPECTRA OF TYPE Ia SN 2014J IN M82 SPANNING THE FIRST 4 MONTHS

We present a time series of 8 - 13 $\mu$m spectra and photometry for SN 2014J obtained 57, 81, 108, and 137 d after the explosion using CanariCam on the Gran Telescopio Canarias. This is the first mid-IR time series ever obtained for a Type Ia supernova. These observations can be understood within the framework of the delayed detonation model and the production of $\sim$0.6 $\rm M_\odot$ of $^{56}$Ni, consistent with the observed brightness, the brightness decline relation, and the $\gamma$-ray fluxes. The [Co III] line at 11.888 $\mu$m is particularly useful for evaluating the time evolution of the photosphere and measuring the amount of $^{56}$Ni and thus the mass of the ejecta. Late-time line profiles of SN 2014J are rather symmetric and not shifted in the rest frame. We see Argon emission, which provides a unique probe of mixing in the transition layer between incomplete burning and nuclear statistical equilibrium. We may see [Fe III] and [Ni IV] emission, both of which are observed to be substantially stronger than indicated by our models. If the latter identification is correct, then we are likely observing stable Ni, which might imply central mixing. In addition, electron capture, also required for stable Ni, requires densities larger than $\sim$$1 \times 10^9$ g cm$^{-3}$, which are expected to be present only in white dwarfs close to the Chandrasekhar limit. This study demonstrates that mid-IR studies of Type Ia supernovae are feasible from the ground and provide unique information, but it also indicates the need for better atomic data.

Detection of a Noble Gas Molecular Ion, 36 ArH + , in the Crab Nebula

Noble gas molecules have not hitherto been detected in space. From spectra obtained with the Herschel Space Observatory, we report the detection of emission in the 617.5- and 1234.6-gigahertz J = 1-0 and 2-1 rotational lines of (36)ArH(+) at several positions in the Crab Nebula, a supernova remnant known to contain both molecular hydrogen and regions of enhanced ionized argon emission. Argon-36 is believed to have originated from explosive nucleosynthesis in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the product of such a supernova event, confirms this expectation. The likely excitation mechanism for the observed (36)ArH(+) emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per centimeter cubed.

Influence of Dissipation Power in Copper Sputtering Plasma Measured by Optical Emission Spectroscopy

Copper oxide is a low cost material, easy process fabrication and sensitivity to ambient conditions. Therefore, it is a suitable p-type semiconductor oxides material to be used as a gas sensing material. In order to raise the sensitivity of the copper oxide gas sensor, study on the correspondence in between the coated thin film with coating parameters is an important part. In current study, optical emission spectroscopy is used to investigate the reactive magnetron sputtering plasma during the deposition of copper oxide thin film. The measurement point was focused at roughly 2cm above the substrate holder. The emission of copper, oxygen and argon in the reactive magnetron sputtering were observed at various plasma conditions. In general, the emission of copper, oxygen and argon increased when the discharge rf power is increased. On the other hand, oxygen line intensity was found to be excess when the oxygen flow rate is above 8sccm. The result suggests the best condition to deposit the copper oxide thin film using solid 3 copper target.

Further insights into prepeak emission in pulsed radiofrequency glow discharge

Side-on optical emission measurements, with spatial and temporal resolution, have been carried out on a modified Grimm type pulsed rf glow discharge, using a copper sample and argon as discharge gas. In particular, the early ignition phase of the pulsed discharge, prepeak, and the beginning of the plateau have been electrically characterized and spectroscopically evaluated along the plasma plume for several argon and copper emission lines. Different pulse repetition frequencies have been used while keeping a constant duty cycle of 25%, covering a range from the μs to the ms pulsed GD. In all the cases a spatially extended discharge has been observed during the first 10–20μs of the pulse, when the dc bias voltage has not been fully established yet. During this early phase of the pulse, the species present in the chamber are excited following the amplitude of the voltage symmetrical oscillations, and argon and copper emission can be detected at all the distances evaluated along the plasma axis at delays as short as 4μs. After the first 20μs approximately, the discharge has contracted close to the sample surface, the dc bias voltage has been almost established and the sputtering process is taking place. Emission registered through side-on observation, at positions relatively far from the sample, decreases and then progressively increases to reach a plateau if the voltage pulse lasts long enough. Moreover, the further the detection position is from the sample surface, the later the increase of the copper and argon emission is observed. Therefore transport phenomena involving both argon and copper species are now evidently leading to an estimated average speed of 100m/s.Additionally, end-on optical emission measurements have been carried out to evaluate the prepeak emission from the negative glow region close to the sample surface, and then to compare this emission with that occurring at farther positions (side-on detection experiments). The results have shown that the basis of both prepeaks might be different as the prepeak signal measured using end-on detection peaks around 10μs later than that observed using side-on detection.

Solid sampling ETV-ICP-OES to study the distribution of elements in clay and soil samples for mineral exploration

A simple and fast method, using solid sampling electrothermal vapourization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES), was developed to determine the distribution of elements in clay separates and soil samples from across the Talbot Lake VMS Cu-Zn prospect, in the Flin Flon-Snow Lake terrane, Manitoba, Canada in order to locate the undercover ore deposit, which is buried under Palaeozoic dolomites and Quaternary till. In the development of the method, the mass of sample, the mass of carrier agent (polytetrafluoroethylene, PTFE) or flow rate of reactant gas (dichlorodifluoromethane (R12)), the carrier and bypass gas flow rates and the temperature program were optimised. Under optimal conditions and with a four-step ETV temperature program, the distribution of the pathfinder elements (Zn, P, S and I) in clay separates and soils showed clear anomalies at 400 and 650 m. The results for Zn and P are in very good agreement with results obtained, following aqua regia (AR) digestion, by ICP mass spectrometry (ICP-MS) by Anglo American Exploration Division (AA-ED). Moreover, the distributions of S and I could be precisely determined (these elements were not reported in the AA-ED study). Using 0–4 mg of AA-ED S5 standard mixed with 2 mg PTFE or with 4.1 ml/min R12 as reactant gas, and using internal standardisation with an argon emission line, calibration curves were obtained that, when applied to Talbot clay separates and soil samples, yielded Zn, S and P concentrations in agreement with AR-ICP-MS results previously obtained by AA-ED. Hence, ETV-ICP-OES completely eliminates the need for clay separation and for extraction or digestion of samples prior to analysis, which significantly simplifies the analysis of geochemical exploration samples.

Tomographic imaging system for measuring impurity line emission in a field-reversed configuration

A 16 chord optical tomography system has been developed and implemented in the flux coil generated-field reversed configuration (FRC). The chords are arranged in two fans of eight, which cover ~35% of the vessel area at the midplane. Each illuminate separate photomultiplier tubes (PMTs) which are fitted with narrow band-pass filters. In this case, filters are centered at 434.8 nm to measure emission from singly ionized argon. PMT crosstalk is negligible. Background noise due to electron radiation and H(γ) line radiation is <10% of argon emission. The spatial resolution of the reconstruction is 1.5 cm. Argon is introduced using a puff valve and tube designed to impart the gas into the system as the FRC is forming. Reconstruction of experimental data results in time-dependent, 2D emissivity profiles of the impurity ions. Analysis of these data show radial, cross-field diffusion to be in the range of 10-10(3) m(2)∕s during FRC equilibrium.

Influence of self-absorption on plasma diagnostics by emission spectral lines

Accurate optical emission spectroscopy (OES) measurements are necessary for plasma semiconductor processing and for optical emission analysis. In this paper we investigate the effects of self-absorption on the most important neutral Argon spectra lines. One of these Argon spectral lines (750 nm) is frequently used for actinometry. The experiment is performed in a reactive ion etch (RIE) capacitively coupled plasma (CCP) system. A comprehensive design of experiments has been created to establish all plasma conditions, power, pressure and gas flow rate which affect the Argon emission intensity by self-absorption. The results are then compared to theoretical calculated line ratios.

Wave numbers and pressure-induced shifts of Ar I atomic lines measured by Fourier transform spectroscopy

Wave numbers and pressure-induced shifts of 19 blue argon emission lines belonging to the 3p56p–3p54s and 3p55p–3p54s transition arrays were measured with high accuracy using a UV/visible Fourier transform spectrometer (FTS). The measurements were made using electrodeless lamps containing traces of 198Hg and argon at pressures of 33 Pa (1/4 Torr), 400 Pa (3 Torr), 933 Pa (7 Torr) and 1333 Pa (10 Torr). Calibration of the FTS wave number scale was obtained using the four most prominent lines of 198Hg as internal standards. The pressure-induced shifts of the argon emission lines are in reasonable agreement with theoretical predictions. These results are of importance for astronomers and analytical chemists who use argon lines for practical wavelength standards as well as for theoreticians calculating argon–argon interactions and potential energy curves of diatomic argon molecules.

Spatial emission distribution of a pulsed radiofrequency glow discharge: Influence of the pulse frequency

A pulsed radiofrequency Glow Discharge (pulsed rf GD) plasma has been spectroscopically characterized by performing side-on measurements of the emitted radiation. The effect of varying the pulse frequency (e.g. between 100 and 10,000Hz), while keeping the duty cycle constant at 25%, has been investigated on different argon and analyte (i.e. copper) emission lines, at different plasma locations. In particular, it is observed that an intermediate frequency of 2.5kHz favors the excitation of the argon atoms, while the argon ions are preferably excited by lower frequencies (e.g. longer pulse widths). Moreover, the excitation of copper atoms has a strong dependence on the upper energy level, and it has been noticed that the emission from higher levels is favored by the use of lower pulsed-rf frequencies. On the other hand, it has been found that the spatial distribution of the gas species and the analyte species (i.e. Ar and Cu, respectively) differ from each other: the atomic argon emission extends longer along the plasma plume than the atomic copper emission. Furthermore, ionic species have their maximum emission signal in the region close to the anode; however, their emission signal decay quite fast at increasing distances to the anode. Nevertheless, it should be highlighted that it is possible to detect ionic emission at distances far away from the negative glow; in regions where usually the sampler cone interface is placed in GD-MS instruments.

Argon 420.1–419.8 nm emission line ratio for measuring plasma effective electron temperatures

We explore the feasibility of using the ratio of two argon emission line intensities at 420.1 and 419.8 nm to measure the effective electron temperature in argon-containing plasmas. Experimental measurements in numerous plasma sources reveal the ratio varies from a value of approximately 1 at high electron temperatures, to a value near 4 at low electron temperatures. This variation is understood in terms of the magnitudes of the electron excitation cross sections into the upper energy levels of the two transitions. At high electron temperatures, the upper levels of the two emission lines, the J = 3 3p9 level for the 420.1 nm line and the J = 0 3p5 level for the 419.8 nm line, are both primarily populated by excitation from the ground state and have similar optical emission cross sections. At low electron temperatures, excitation is dominated by excitation from the metastable levels which have very different cross sections into the two levels. Temperatures obtained with this line pair ratio in an inductively coupled plasma are found to be consistent with values obtained from a Langmuir probe as well as an analysis of the entire set of 2px → 1sy emission lines (665–1150 nm) under a wide variety of plasma conditions.

Study on Start Burning Performance of Micro-ICP Using Stereo Spiral Coil

According to the problem of low energy utilization of plane spiral coil used in micro-ICP, a kind of micro stereo helical coil was designed. Made 24 different structural parameters of stereo spiral coil whose diameter range 3~10 mm. Using comprehensive experimental method tested different parameters’ coils inspire argon plasma. In 13.56MHz RF power, relationships between argon pressure, coil turns, coil diameter and combustion /maintaining power of micro-ICP excitation source were tested. From spectrometer observed 17 argon emission spectrum in 690~860 nm. Spectral lines intensity influenced by RF power and work pressure. Experiments proved that micro-ICP excitation source using stereo helical coil is feasible. It can form Ar plasma and inspire Ar spectral lines.