Showing papers on "Argon published in 2012"
TL;DR: For example, Pujol et al. as mentioned in this paper proposed that the Earth is not as volatile-poor as previously thought, and showed that it contains up to 2 (± 1) % contribution of carbonaceous chondrite (CI-CM) to a dry proto-Earth.
805 citations
TL;DR: In this paper, the authors examined 17-4 PH stainless steel powders produced by atomization in either argon or nitrogen atmospheres and correspondingly fabricated by selective laser melting (SLM) in either a nitrogen or argon atmosphere.
Abstract: Objective This research examines 17-4 PH stainless steel powders produced by atomization in either argon or nitrogen atmospheres (producing martensitic (α-Fe) or mostly austenitic (γ-Fe) phase powders, respectively) and correspondingly fabricated by selective laser melting (SLM) in either a nitrogen or argon atmosphere. Methods Pre-alloyed 17-4 stainless steel powders prepared by atomization in either argon or nitrogen atmospheres were fabricated by SLM. The initial powder microstructures and phase structures were examined by light (optical) microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Prototypes fabricated by SLM were similarly characterized, and in addition transmission electron microscopy (TEM) characterization was also performed. Results Martensitic powder fabricated by SLM in nitrogen gas produced a martensitic product while pre-alloyed austenitic powder produced a primarily austenitic product. In contrast, both powders produced martensitic products when fabricated by SLM in argon gas. This unusual behavior occurred because of the rapid cooling affected by nitrogen versus argon cover gas as a consequence of a 40% greater thermal conductivity of nitrogen gas versus argon gas. SLM fabricated martensitic products exhibited HRC 30 in contrast to HRC 43 when aged at 482°C for 1 hour. Austenitic products did not exhibit age-hardening. Conclusions Using an argon cover gas, SLM-fabricated products are martensitic (and magnetic) with either an austenitic or martensitic pre-alloyed 17-4 PH stainless steel powder. Using a nitrogen cover gas, the product phase is the same as the precursor powder phase (austenitic or martensitic).
306 citations
TL;DR: In this article, a series of activated carbons with ranging porosity (burn-off) have been prepared from olive stones using CO2 as activating agent and characterized using nitrogen and argon adsorption at low temperature (77.4 K for N2 and 87.3 K for Ar).
130 citations
TL;DR: A direct correlation between the film density and band gap in nanocrystalline WO(3) films is established on the basis of the observed results.
Abstract: Nanocrystalline WO3 thin films were produced by sputter-deposition by varying the ratio of argon to oxygen in the reactive gas mixture during deposition. The surface chemistry, physical characteris...
128 citations
TL;DR: It is observed that electron irradiation, used for charge compensation, can induce molecular damage to areas of the reference samples well beyond the analyzed region that significantly affects molecular secondary-ion intensities in the initial stages of a depth profile in these materials.
Abstract: The depth profiling of organic materials with argon cluster ion sputtering has recently become widely available with several manufacturers of surface analytical instrumentation producing sources suitable for surface analysis. In this work, we assess the performance of argon cluster sources in an interlaboratory study under the auspices of VAMAS (Versailles Project on Advanced Materials and Standards). The results are compared to a previous study that focused on C(60)(q+) cluster sources using similar reference materials. Four laboratories participated using time-of-flight secondary-ion mass spectrometry for analysis, three of them using argon cluster sputtering sources and one using a C(60)(+) cluster source. The samples used for the study were organic multilayer reference materials consisting of a ∼400-nm-thick Irganox 1010 matrix with ∼1 nm marker layers of Irganox 3114 at depths of ∼50, 100, 200, and 300 nm. In accordance with a previous report, argon cluster sputtering is shown to provide effectively constant sputtering yields through these reference materials. The work additionally demonstrates that molecular secondary ions may be used to monitor the depth profile and depth resolutions approaching a full width at half maximum (fwhm) of 5 nm can be achieved. The participants employed energies of 2.5 and 5 keV for the argon clusters, and both the sputtering yields and depth resolutions are similar to those extrapolated from C(60)(+) cluster sputtering data. In contrast to C(60)(+) cluster sputtering, however, a negligible variation in sputtering yield with depth was observed and the repeatability of the sputtering yields obtained by two participants was better than 1%. We observe that, with argon cluster sputtering, the position of the marker layers may change by up to 3 nm, depending on which secondary ion is used to monitor the material in these layers, which is an effect not previously visible with C(60)(+) cluster sputtering. We also note that electron irradiation, used for charge compensation, can induce molecular damage to areas of the reference samples well beyond the analyzed region that significantly affects molecular secondary-ion intensities in the initial stages of a depth profile in these materials.
127 citations
TL;DR: In this article, two-photon absorption laser-induced fluorescence (TALIF) spectroscopy measurements are performed in a cold argon/oxygen atmospheric pressure plasma jet.
Abstract: By investigating the atomic oxygen density in its effluent, two-photon absorption laser-induced fluorescence (TALIF) spectroscopy measurements are for the first time performed in a cold argon/oxygen atmospheric pressure plasma jet. The measurements are carried out in ambient air and quenching by inflowing air species is considered. We propose a novel absorption technique in the VUV spectral range, where emission originating from within the discharge is used as light source to determine the inflow of atmospheric oxygen into the effluent. Furthermore, we propose a modelling solution for the on-axis density of inflowing ambient air based on the stationary convection?diffusion equation.
114 citations
TL;DR: In this article, the presence of plasma bullets in a MHz argon atmospheric pressure plasma jet was confirmed by phase-resolved optical emission measurements, and the ozone production rates were investigated by two independent diagnostic techniques yielding complementary results.
Abstract: This study for the first time confirms the presence of plasma bullets in a MHz argon atmospheric pressure plasma jet. Bullet characteristics are investigated by phase-resolved optical emission measurements. Regarding the jet's reactive component output, its ozone production rates are investigated by two independent diagnostic techniques yielding complementary results. The first method—UV-absorption spectroscopy in the Hartley band—determines space-resolved distribution of the ozone concentration in the jet effluent. The second method—quantum cascade laser-absorption spectroscopy in the mid-infrared spectral region—yields high sensitivity results of the average ozone concentration in a multipass cell, in which the effluent is directed. The results of both diagnostic techniques show excellent agreement.
102 citations
TL;DR: MAGPIE as discussed by the authors is a helicon source plasma device operating in a magnetic hill configuration designed to support a broad range of research activity and is the first stage of the Materials Diagnostic Facility at the Australian National University.
Abstract: The Magnetized Plasma Interaction Experiment (MAGPIE) is a versatile helicon source plasma device operating in a magnetic hill configuration designed to support a broad range of research activity and is the first stage of the Materials Diagnostic Facility at the Australian National University. Various material targets can be introduced to study a range of plasma–material interaction phenomena.Initially, with up to 2.1 kW of RF at 13.56 MHz, argon (1018–1019 m−3) and hydrogen (up to 1019 m−3 at 20 kW) plasma with electron temperature ∼3–5 eV was produced in magnetic fields up to ∼0.19 T. For high mirror ratio we observe the formation of a bright blue core in argon above a threshold RF power of 0.8 kW. Magnetic probe measurements show a clear m = +1 wave field, with wavelength smaller than or comparable to the antenna length above and below this threshold, respectively. Spectroscopic studies indicate ion temperatures <1 eV, azimuthal flow speeds of ∼1 km s−1 and axial flow near the ion sound speed.
93 citations
TL;DR: Time-resolved tunable diode-laser absorption spectroscopy measurements were performed on the argon metastable (Ar-m) level 3s(2)3p(5)(P-2(3/2)degrees)4s excited at 801.478 nm, in the dense plasma r...
Abstract: Time-resolved tunable diode-laser absorption spectroscopy measurements were performed on the argon metastable (Ar-m) level 3s(2)3p(5)(P-2(3/2)degrees)4s excited at 801.478 nm, in the dense plasma r ...
92 citations
TL;DR: In this paper, a two-temperature chemically non-equilibrium model describing in a selfconsistent manner the heat transfer, the plasma chemistry, the electric and magnetic field in a high-current free-burning arc in argon has been developed.
Abstract: A two-temperature chemically non-equilibrium model describing in a self-consistent manner the heat transfer, the plasma chemistry, the electric and magnetic field in a high-current free-burning arc in argon has been developed. The model is aimed at unifying the description of a thermionic tungsten cathode, a flat copper anode, and the arc plasma including the electrode sheath regions. The heat transfer in the electrodes is coupled to the plasma heat transfer considering the energy fluxes onto the electrode boundaries with the plasma. The results of the non-equilibrium model for an arc current of 200 A and an argon flow rate of 12 slpm are presented along with results obtained from a model based on the assumption of local thermodynamic equilibrium (LTE) and from optical emission spectroscopy. The plasma shows a near-LTE behaviour along the arc axis and in a region surrounding the axis which becomes wider towards the anode. In the near-electrode regions, a large deviation from LTE is observed. The results are in good agreement with experimental findings from optical emission spectroscopy.
91 citations
TL;DR: In this paper, a coal sample was analyzed using a 266 nm Nd:YAG laser in different gas environments (air, argon and helium) at atmospheric pressure and the influence of the ambient gas on the laser-induced coal plasma was studied by using time-resolved analysis.
Abstract: Laser ablation chemical analysis of a coal sample was studied by LIBS (laser-induced breakdown spectroscopy). Ablation was performed using a 266 nm Nd:YAG laser in different gas environments (air, argon and helium) at atmospheric pressure. We present characteristics of spectra measured from coal with special attention to atomic and molecular carbon including CI, C2 and CN. The influence of the ambient gas on the laser-induced coal plasma was studied by using time-resolved analysis. Atomic iron emission lines were employed to construct Boltzmann plots for the plasma excitation temperature. Computer simulations of C2 spectra were used to deduce the molecular rotational temperature. Electron density and total atomic and molecular number density are reported to describe emission differences of atomic and molecular carbon in the different gas environments. These data demonstrate that the plasma excitation temperature is the primary factor contributing to differences among the atomic carbon emission in the gas environments. Reactions between the plasma species and ambient gas, and the total molecular number are main factors influencing molecular carbon emission. Finally, the influence of laser energy on the rotational temperature was studied in the air environment to demonstrate that the rotational temperature derived from C2 band emission can be utilized to correct plasma fluctuations.
TL;DR: In this paper, the effect of different gases and their pressures on the intensity of spectral emission, electron temperature and density of the laser-produced plasma has been investigated, and the dependence of surface morphological changes of an irradiated target on the nature and pressure of an ambient gas has been revealed.
Abstract: The ablation of Cd has been performed by employing Q-switched Nd: YAG 10 ns laser pulses with a central wavelength of 1064 nm for a pulsed energy of 200 mJ under various ambient environments of argon, air and helium. The optical emission spectroscopy of Cd plasma has been studied under different filling pressures of shield gases ranging from 5 torr to 760 torr using LIBS spectrometer system. The effect of different gases and their pressures on the intensity of spectral emission, electron temperature and density of the laser-produced plasma has been investigated. SEM analysis has been performed to investigate the dependence of surface morphological changes of an irradiated target on the nature and pressure of an ambient gas. A strong correlation has revealed the vital role of electron temperature and density of laser-induced plasma for the surface modification of Cd. These results strongly indicate that the nature and pressure of the ambient atmosphere is one of the controlling factors of the plasma characteristics, as well as the factors related to the laser energy absorption for surface modification.
TL;DR: In this paper, an atmospheric pressure plasma jet (APPJ) was used to modify polytetrafluoroethylene (PTFE) surface properties, which is the most promising one and therefore, an APJ was used in this work to modify PTFE samples.
Abstract: Polytetrafluoroethylene (PTFE) has many successful engineering applications due to its great chemical stability. However, for some industrial applications, the poor adhesion of PTFE to other materials is a disadvantage. To extend the PTFE application range, several methods have been developed to modify its surface properties. Among these different techniques, plasma surface modification is the most promising one and therefore, an atmospheric pressure plasma jet (APPJ) will be used in this work to modify PTFE samples. Two different discharge gasses have been used: pure argon and an argon/CO 2 mixture and both plasma jets have been examined with optical emission spectroscopy to identify the plasma species present in the discharge. From these results, it was found that the discharge in argon contains argon atoms, nitrogen molecules and metastables, atomic oxygen and OH radicals, while the argon/CO 2 discharge contains also radicals containing CO groups. In a second part of the work, the chemical and physical changes induced by both discharges on PTFE surfaces have been investigated using contact angle measurements, SEM, AFM and XPS. From these results, it was found that exposure times below 20 s lead to a small contact angle decrease due to the introduction of a small amount of oxygen. In contrast, at higher treatment times, the contact angle starts to increase again due to advanced chain scissions leading to a high amount of oligomeric segments on the PTFE surface. As a result of these surface degradation processes, the wettability of PTFE could not be greatly enhanced, however, in the near future, it will be investigated whether these degradation reactions can be eliminated.
TL;DR: The model describes in a self-consistent manner the gas flow and heat transfer, the in-coupling of the microwave energy into the plasma, and the reaction kinetics relevant to high-pressure argon plasma including the contribution of molecular ion species.
Abstract: A two-dimensional model of microwave-induced plasma (field frequency 2.45 GHz) in argon at atmospheric pressure is presented. The model describes in a self-consistent manner the gas flow and heat transfer, the in-coupling of the microwave energy into the plasma, and the reaction kinetics relevant to high-pressure argon plasma including the contribution of molecular ion species. The model provides the gas and electron temperature distributions, the electron, ion, and excited state number densities, and the power deposited into the plasma for given gas flow rate and temperature at the inlet, and input power of the incoming TEM microwave. For flow rate and absorbed microwave power typical for analytical applications (200-400 ml/min and 20 W), the plasma is far from thermodynamic equilibrium. The gas temperature reaches values above 2000 K in the plasma region, while the electron temperature is about 1 eV. The electron density reaches a maximum value of about 4 × 10(21) m(-3). The balance of the charged particles is essentially controlled by the kinetics of the molecular ions. For temperatures above 1200 K, quasineutrality of the plasma is provided by the atomic ions, and below 1200 K the molecular ion density exceeds the atomic ion density and a contraction of the discharge is observed. Comparison with experimental data is presented which demonstrates good quantitative and qualitative agreement.
TL;DR: In this paper, the effect of different gases and their pressures on the intensity of spectral emission, electron temperature and density of laser-produced plasma has been investigated, and the results obtained strongly indicate that the nature and pressure of the ambient atmosphere are one of the controlling factors of the plasma characteristics.
Abstract: The effect of different gases and their pressures on the intensity of spectral emission, electron temperature and density of laser-produced plasma has been investigated. For this purpose, Cu targets were ablated by employing Q-switched Nd:YAG laser pulses (λ~1064 nm, τ~10 ns, pulsed energy of 200 mJ) under various filling pressures of the background gases argon, air and helium. The optical emission spectroscopy of Cu plasma has been studied using the laser-induced breakdown spectroscopy system. The results obtained strongly indicate that the nature and pressure of the ambient atmosphere are one of the controlling factors of the plasma characteristics. A scanning electron microscopy analysis has been performed to investigate the dependence of surface morphological changes of an irradiated target on the nature and pressure of an ambient gas. The basic aim of this study is to improve the understanding of ablation mechanisms and plasma parameters (optical emission intensity, electron temperature and density) under various ambient conditions. The optimization of experimental conditions (the nature and pressure of the ambient environment) is very important for temperatures and densities of ablated species, which are consequently crucial for pulsed laser deposition of thin films and nanostructuring of materials.
TL;DR: In this paper, three major elements, carbon, hydrogen, and nitrogen, in twenty-four bituminous coal samples, were measured by laser-induced breakdown spectroscopy Argon and helium were applied as ambient gas to enhance the signals and eliminate the interference of nitrogen from surrounding air.
Abstract: Three major elements, carbon, hydrogen, and nitrogen, in twenty-four bituminous coal samples, were measured by laser-induced breakdown spectroscopy Argon and helium were applied as ambient gas to enhance the signals and eliminate the interference of nitrogen from surrounding air The relative standard deviation of the related emission lines and the performance in the partial least squares (PLS) modeling were compared for different ambient environments The results showed that argon not only improved the intensity, but also reduced signal fluctuation The PLS model also had the optimal performance in multi-element analysis using argon as ambient gas The root mean square error of prediction of carbon concentration decreased from 425% in air to 349% in argon, while the average relative error reduced from 496% to 298% Hydrogen line demonstrated similar improvement Yet, the nitrogen lines were too weak to be detected even in an argon environment which suggested the nitrogen signal measured in air come from the breakdown of nitrogen molecules in the atmosphere
TL;DR: In this article, two concentric dielectric barriers, a short plasma zone with a wide discharge gap have been used to investigate methane conversion in reactors employing alumina and quartz as dielectrics.
TL;DR: It is suggested that crystallization of perovskite from a magma ocean in the very early stages of Earth’s history concentrated argon in the lower mantle, whereas the xenon solubility in MgSiO3 perovSkite is orders of magnitude lower.
Abstract: The solubility of argon in lower mantle minerals is shown to be much higher than for xenon, so that the depletion of xenon relative to argon in Earth’s atmosphere can be explained by mantle degassing. The noble gas xenon is strongly depleted relative to argon in the atmospheres of both Earth and Mars, when compared with the abundances in chondritic meteorites, which are generally considered to be indicators of early Solar System geochemistry. Here, Svyatoslav Shcheka and Hans Keppler offer a possible explanation for this apparent anomaly. They show that more than 1 wt% of argon can be dissolved in the abundant lower-mantle mineral perovskite (MgSiO3), but that xenon solubility in perovskite is orders of magnitude lower. Thus the crystallization of perovskite from a magma ocean in the very early stages of Earth's history could have concentrated argon in the lower mantle, with xenon being lost along with the early Earth's atmosphere. The argon from the lower mantle was then gradually released into Earth's atmosphere, explaining its abundance relative to xenon. In the atmospheres of Earth and Mars, xenon is strongly depleted relative to argon, when compared to the abundances in chondritic meteorites1,2. The origin of this depletion is poorly understood3,4,5,6,7,8,9,10,11,12,13. Here we show that more than one weight per cent of argon may be dissolved in MgSiO3 perovskite, the most abundant phase of Earth’s lower mantle, whereas the xenon solubility in MgSiO3 perovskite is orders of magnitude lower. We therefore suggest that crystallization of perovskite from a magma ocean in the very early stages of Earth’s history concentrated argon in the lower mantle. After most of the primordial atmosphere had been lost, degassing of the lower mantle replenished argon and krypton, but not xenon, in the atmosphere. Our model implies that the depletion of xenon relative to argon indicates that perovskite crystallized from a magma ocean in the early history of Earth and perhaps also Mars.
TL;DR: A kinematic scattering model is applied to interpret the effective surface mass and energy transfer when atoms strike two different surfaces under identical bombardment conditions to identify trends that could lead to a robust general understanding of energy transfer processes induced by collisions of gas-phase species with liquid and semi-solid surfaces.
Abstract: We have conducted investigations of the energy transfer dynamics of atomic oxygen and argon scattering from hydrocarbon and fluorocarbon surfaces. In light of these results, we appraise the applicability and value of a kinematic scattering model, which views a gas-surface interaction as a gas-phase-like collision between an incident atom or molecule and a localized region of the surface with an effective mass. We have applied this model to interpret the effective surface mass and energy transfer when atoms strike two different surfaces under identical bombardment conditions. To this end, we have collected new data, and we have re-examined existing data sets from both molecular-beam experiments and molecular dynamics simulations. We seek to identify trends that could lead to a robust general understanding of energy transfer processes induced by collisions of gas-phase species with liquid and semi-solid surfaces.
TL;DR: In this paper, three types of gases, pure argon (99.999%), argon with 2% oxygen, and argon and 10% nitrogen, were used as operating gases of a direct current atmospheric pressure cold plasma jet to inactivate Staphylococcus aureus suspended in a liquid.
Abstract: Three types of gases, pure argon (99.999%), argon with 2% oxygen, and argon with 2% oxygen and 10% nitrogen were used as operating gases of a direct current atmospheric pressure cold plasma jet to inactivate Staphylococcus aureus (S. aureus) suspended in a liquid. The inactivation efficacies for the plasma jets operating in the three gases decrease from Ar/O2(2%) to Ar/O2(2%)/N2(10%) to pure Ar. Optical emission spectroscopy, electron spin resonance spectroscopy, high performance liquid chromatography, and atomic absorption spectrophotometry were employed to identify and monitor the reactive species in the plasma-liquid system for the three operating gases and revealed the presence of O, 1O2, OH, NO, H2O2, O3, and NO3−/NO2− as well as Cu+/Cu2+. The S. aureus inactivation results indicate that atomic oxygen (O) is the key inactivation agent, while other species play a lesser role in the inactivation progress studied here.
TL;DR: In this paper, the authors constrain the bulk content of Titan's interior for various gas species (CH4, CO2, CO, NH3, H2S, Ar, Ne, Xe), and show that most of the gas compounds initially incorporated within Titan are likely stored dissolved in the subsurface water ocean.
Abstract: In the present report, by using a series of data gathered by the Cassini-Huygens mission, we constrain the bulk content of Titan's interior for various gas species (CH4, CO2, CO, NH3, H2S, Ar, Ne, Xe), and we show that most of the gas compounds (except H2S and Xe) initially incorporated within Titan are likely stored dissolved in the subsurface water ocean. CO2 is likely to be the most abundant gas species (up to 3% of Titan's total mass), while ammonia should not exceed 1.5 wt%. We predict that only a moderate fraction of CH4, CO2, and CO should be incorporated in the crust in the form of clathrate hydrates. By contrast, most of the H2S and Xe should be incorporated at the base of the subsurface ocean, in the form of heavy clathrate hydrates within the high-pressure ice layer. Moreover, we show that the rocky phase of Titan, assuming a composition similar to CI carbonaceous chondrites, is a likely source for the noble gas isotopes (40Ar, 36Ar, 22Ne) that have been detected in the atmosphere. A chondritic core may also potentially contribute to the methane inventory. Our calculations show that a moderate outgassing of methane containing traces of neon and argon from the subsurface ocean would be sufficient to explain the abundance estimated by the Gas Chromatograph Mass Spectrometer. The extraction process, implying partial clathration in the ice layers and exsolvation from the water ocean, may explain why the 22Ne/36Ar ratio in Titan's atmosphere appears higher than the ratio in carbonaceous chondrites.
TL;DR: In this article, a model was used to quantify the impact of buffer gas on the energy and the incidence angle distributions of the deposited W and Se atoms, depending on the efficiency of the preferential sputtering of Se atoms.
TL;DR: In this article, the changes to the surface composition and work function induced by argon sputter cleaning and oxygen plasma treatments were characterized using x-ray photoelectron spectroscopy, ultraviolet photo-electron Spectroscopy and density functional theory modelling.
Abstract: Zinc oxide (ZnO) films were grown by radio frequency magnetron sputter deposition and the changes to its surface composition and workfunction induced by argon sputter cleaning and oxygen plasma treatments were characterized using x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and density functional theory modelling. Compared with a workfunction of 3.74?eV for the as-deposited ZnO films, a workfunction of 3.95?eV was obtained after Ar sputter cleaning and 4.21?eV after exposure to oxygen plasma. The data indicate that oxygen plasma treatment leads to a more negative ZnO surface. The dipole induced by this charge redistribution reinforces the original surface dipole, which results in an increase in the surface dipole moment and an increase in workfunction. The reverse is true for hydrocarbon contamination of ZnO surfaces. Excellent qualitative agreement between the experimental results and computational modelling was obtained. The results suggest that specific surface functionalization may be a viable method of controlling the workfunction of ZnO for use as the transparent conducting oxide in optoelectronic applications such as solar cells and organic light-emitting diodes.
TL;DR: In this article, the axial phase model parameters of AECS PF-2 were found by matching the measured and calculated current waveforms over a range of pressures, and the results showed a value of fm = 0.05 ± 0.7 for both Argon and Neon.
Abstract: For the plasma focus device AECS PF-2 operated in Ar and INTI PF in Ne, model parameters of mass and current in the axial phase of plasma focus were found by matching the measured and calculated current waveforms over a range of pressures. The results show a value of fm = 0.05 ± 0.01 over 0.2–1.2 Torr in Ar; and fm = 0.04 ± 0.01 over 0.7–4.1 Torr in Neon. The value of fc = 0.7 was fitted for all cases. Combining these results with those published for several other small machines it would appear that, where measured current waveforms are not available for example in designing new machines, a good compromise would be to take a guideline value of fm = 0.05 and fc = 0.7 for both Argon and Neon.
TL;DR: In this article, the authors demonstrate that the difference in absorption rate between UV and IR radiations leads to different propagation behaviors of the plasma produced with these radiations, leading to higher electron density and temperature.
Abstract: Laser-induced plasma from an aluminum target in one-atmosphere argon background has been investigated with ablation using nanosecond ultraviolet (UV: 355 nm) or infrared (IR: 1064 nm) laser pulses. Time- and space-resolved emission spectroscopy was used as a diagnostics tool to have access to the plasma parameters during its propagation into the background, such as optical emission intensity, electron density, and temperature. The specific feature of nanosecond laser ablation is that the pulse duration is significantly longer than the initiation time of the plasma. Laser-supported absorption wave due to post-ablation absorption of the laser radiation by the vapor plume and the shocked background gas plays a dominant role in the propagation and subsequently the behavior of the plasma. We demonstrate that the difference in absorption rate between UV and IR radiations leads to different propagation behaviors of the plasma produced with these radiations. The consequence is that higher electron density and tem...
TL;DR: In this paper, the authors report on the observation of enhanced high harmonics from a carbon plasma using sub-5-fs laser pulses, which can be attributed to the presence of carbon nanoparticles in the ablation plumes.
Abstract: We report on the observation of enhanced high harmonics from a carbon plasma using sub-5-fs laser pulses. The efficiency of harmonic generation in the range of 14\char21{}25 eV was up to five times higher in the case of a plasma medium (graphite ablation) compared with gas (argon) under similar experimental conditions. The harmonic enhancement can be attributed to the presence of carbon nanoparticles in the ablation plumes.
04 Apr 2012
TL;DR: In this article, a collisional-radiative (CR) model is used to predict the emission of the excited electronic states of nitrogen (N2 B3Πg, N2 C3 Πu) and the nitrogen ion N 2 + B 2 Σ u +.
Abstract: An atmospheric pressure nitrogen/argon plasma flows at high velocity through a water-cooled test-section in which it is forced to recombine within 250 μs. At the test-section inlet, the plasma is in Local Thermodynamic Equilibrium (LTE) at about 7200 K. Because recombination rates are finite, the plasma reaches a state of chemical nonequilibrium at the exit of the test-section, at a temperature of about 4715 K. At the test-section exit, the radiation emitted by the plasma, measured by emission spectroscopy, shows significant departures from equilibrium in the populations of the excited electronic states of nitrogen (N2 B3Πg, N2 C3Πu) and of the nitrogen ion N 2 + B 2 Σ u + . This experiment is thus proposed as a test-case to validate collisional-radiative (CR) models. A vibrationally specific CR model is then used to predict the emission of these states. The rate coefficients of the model are calculated with the Weighted Rate Coefficient method based on elementary cross-section data. These rates depend explicitly on the kinetic temperatures of electrons (Te) and heavy species (Tg). The predictions of the CR model are in good agreement with the measured vibrational population distribution in the N2 B state. A method is then proposed to determine ground state nitrogen atom densities based on the measured vibrational population distribution of the N2 B state.
TL;DR: In this article, a non-local approach for using Langmuir probes in the presence of magnetic fields in the range 0.015-0.079 T was proposed, where the electron part of the currentvoltage probe characteristics was used to obtain the plasma potential, the electron energy distribution function (EEDF), the electron temperature and the electron density.
Abstract: In this work, methods for using Langmuir probes (LPs) in magnetized plasmas are presented. The electron part of the current–voltage probe characteristics is used to obtain the plasma potential, the electron energy distribution function (EEDF), the electron temperature and the electron density. The application of LPs to EEDF evaluation in the presence of magnetic fields in the range 0.01–0.1 T is investigated and discussed based on kinetic theory in a non-local approach. Data for EEDFs in magnetic fields in the range 0.015–0.079 T are acquired using current–voltage characteristics measured in low pressure Ar and He dc gas discharges. It is also shown that the EEDFs are Maxwellian up to the energy of the first excited states of argon and helium. The values of the plasma potential, electron temperature and density are evaluated. Comparison of the results obtained with probes perpendicular and parallel to the magnetic field results in satisfactory agreement.The results presented demonstrate that the procedures proposed allow one to acquire the main plasma parameters using the electron part of the current–voltage LP characteristics in magnetized plasmas.
TL;DR: Matrix-isolation experiments and quantum-chemical calculations have led to the characterization of two new compounds, namely first open-shell binary gold fluoride, AuF(2), and a NeAuF complex.
Abstract: Noble with a difference: Matrix-isolation experiments and quantum-chemical calculations have led to the characterization of two new compounds, namely first open-shell binary gold fluoride, AuF(2), and a NeAuF complex. Moreover, ArAuF, AuF(3), Au(2)F(6), and monomeric AuF(5) have been produced and identified under cryogenic conditions in neon and argon matrices.
TL;DR: In this paper, the authors investigated the formation mechanisms for atmospheric pressure plasma jets (APPJ) of He and Ar by comparing the discharge current, light emission from jet, and time-resolved image of the discharge.
Abstract: Formation mechanisms for atmospheric pressure plasma jets (APPJ) of He and Ar are investigated by comparing the discharge current, light emission from jet, and time-resolved image of the discharge. A longer jet of He (Ar) is available with active (ground) electrode sitting at downstream side. The jet of He outside active electrode arises from corona discharge, while that of Ar outside ground electrode results from charge overflow, and can be diffusive or filamentous in different phases of the applied voltage. The underlying mechanisms are discussed. These results can be helpful for the further mechanism investigation and implementation of APPJs.