Showing papers on "Argon published in 1989"
TL;DR: In this article, a collisional-radiative model with an extended region of applicability is developed for an argon atom plasma, taking into account 65 effective levels, and special attention is paid to those determining the set of cross sections for excitation by electrons from the ground state, owing to the possibility of utilizing the formulae recommended in kinetic modelling studies of discharges in argon or in mixtures including argon atoms.
Abstract: A collisional-radiative model with an extended region of applicability is developed for an argon atom plasma. Atom-atom inelastic collisions and diffusion losses of the metastable states along with the electron-atom inelastic collisions and radiative processes are considered in this model, taking into account 65 effective levels. Among the analytical expressions used for the corresponding cross sections, special attention is paid to those determining the set of cross sections for excitation by electrons from the ground state, owing to the possibility of utilising the formulae recommended in kinetic modelling studies of discharges in argon or in mixtures including argon atoms. The numerical method developed makes it possible to investigate the mechanisms by which the excited levels are populated in a non-equilibrium argon plasma characterised (even in the case of a non-Maxwellian electron distribution) by a set of parameters, such as the electron kinetic temperature Te, the atom temperature Ta, the ion temperature Ti, the electron number density ne, the ground state atom population n1, the discharge tube (or the plasma column) radius R and the optical escape factors Lambda mn and Lambda m, which are dependent only on the quantities Ta, n1 and R in many cases of practical interest.
236 citations
TL;DR: In this paper, the observed seasonal cycles of temperature, argon, helium, and oxygen are simulated with an upper ocean model and linearized the model's response to variations in vertical diffusivity, air injection, gas exchange rate, and new production and then used an inverse technique to determine the values of these parameters that best fit the data.
Abstract: Argon measurements, obtained from one year of monthly detailed vertical profiles near Bermuda (32N 64W), show a maximum in argon supersaturation of about 4% in the seasonal thermocline in late summer. Since the argon supersaturation is 3-4 times smaller than that of oxygen, most of the oxygen supersaturation is not of physical origin and hence must result from biological production. In the winter mixed layer, air injection produces argon supersaturation in spite of high gas exchange rates. During spring and summer, radiative heating, air injection, and an upward argon flux create an even larger supersaturation in the mixed layer. In the seasonal thermocline, radiative heating maintains argon concentrations above solubility equilibrium in spite of vertical mixing. The observed seasonal cycles of temperature, argon, helium, and oxygen are simulated with an upper ocean model. We linearized the model's response to variations in vertical diffusivity, air injection, gas exchange rate, and new production and then used an inverse technique (singular value decomposition) to determine the values of these parameters that best fit the data. A vertical turbulent diffusivity of 0.9 ± 0.1 x 10-4 m2 S~I is consistent with both the thermal history and subsurface argon distribution. The rate of air injection, determined to ±25%, is similar to previous estimates. The seasonally-averaged gas exchange rate is 17 ± 12%lower than predicted by Liss and Merlivat (I986). We estimate a lower limit to depth-integrated new production below the mixed layer of 4.3 ± 1.7 moles O2 m-2 yr-I during 1985, and obtain an estimate of 5.6 ± 1.5 moles O2 m-2 yr-I if new production in the mixed layer is fixed at zero.
233 citations
TL;DR: In this paper, a low-pressure microwave-plasma reactor was used for homogeneous nucleation of diamond powder in a variety of hydrocarbons diluted in argon, hydrogen, or oxygen gas mixtures.
Abstract: Homogeneous nucleation of diamond powder is reported. The experiments were performed in a low‐pressure microwave‐plasma reactor. The deposits were collected downstream of the reaction zone and subjected to wet oxidation to remove nondiamond carbons. The residues were analyzed by optical and electron microscopy, electron diffraction, and Raman spectroscopy. A variety of hydrocarbons diluted in argon, hydrogen, or oxygen gas mixtures were tested. In most cases only nondiamond materials, like graphite and carbyne, were obtained. Homogeneous nucleation of diamond was clearly observed in dichloromethane‐ and trichloroethylene‐oxygen mixtures. The particles formed had crystalline shapes, mostly hexagonal. The largest particles were about 0.2 μm, although most of the particles were on the order of 50 nm in diameter. The powder was identified to be a mixture of polytypes of diamond.
169 citations
TL;DR: In this article, high-resolution spectroscopic measurements of H2O vapor in the 720-nm wavelength region were conducted to investigate the broadening and shifting of H 2O lines by air, nitrogen, oxygen, and argon over a wide range of pressures and temperatures.
141 citations
TL;DR: In this article, the electron attachment rate constants for SF6 have been measured in dilute mixtures of SF6 in high pressure (>1 atm) N2, Ar, and Xe buffer gases at room temperature (T≊300 K) over a wide E/N range (electric field strength to gas number density ratio), corresponding to mean electron energies from near thermal electron energies (≊0.04 eV) to 〈e〉≊4.3 eV).
Abstract: The electron attachment rate constants ka for SF6 have been measured in dilute mixtures of SF6 in high pressure (>1 atm) N2, Ar, and Xe buffer gases at room temperature (T≊300 K) over a wide E/N range (electric field strength to gas number density ratio), corresponding to mean electron energies 〈e〉 from near thermal electron energies (≊0.04 eV) to 〈e〉≊4.3 eV. Particular attention has been paid to the effects of space charge distortion, molecular impurities, and changes in the electron energy distribution function on the measured electron attachment rate constant values at the lower E/N values in these mixtures. The present measured thermal electron attachment rate constants in SF6/N2 and SF6/Xe gas mixtures are in excellent agreement with recent accurate measurements of these parameters in several SF6/buffer gas mixtures. At higher 〈e〉 values, the present SF6/N2 measurements are in fair agreement with previous measurements, while no previous measurements using Ar and Xe buffer gases have been published. T...
103 citations
TL;DR: Angular correlations between the three outgoing electrons in the double ionization of argon by electron impact have been measured for the first time and are consistent with a two-step model for thedouble ionization mechanism.
Abstract: Angular correlations between the three outgoing electrons in the double ionization of argon by electron impact have been measured for the first time. Double and triple coincidence techniques are used to determine simultaneously all final electron energies and angles, and provide fourfold and fivefold differential cross sections, respectively. The angular distributions are consistent with a two-step model for the double ionization mechanism. The present results clearly show the feasibility and potentiality of ({ital e},3{ital e}) experiments.
102 citations
TL;DR: In this article, the evolution of luminescence from rare gases was studied as a function of number density, and the energy separation between the fast and slow components was found to be density independent.
Abstract: For the first time, the evolution of luminescence from rare gases was studied as a function of number density. Synchrotron radiation served as a light source for selective and pulsed excitation of the samples. The excitation spectra confirm previous results on perturbed Rydberg states and exciton appearance in dense media. In time‐resolved emission spectra the peak energies and widths of the luminescence bands were followed. The energy separation between the fast and slow components is found to be density independent. A model proposed by Cheshnovsky et al. [Chem. Phys. Lett. 15, 475 (1972)] accounts for the change in peak width with temperature. Both lifetimes decrease with increasing density. The data extrapolate to 3.3±0.1 ns (Ar); 3.4±0.1 ns, 270±5 ns (Kr); 4.5±0.1 ns, 100±5 ns (Xe) for the low density limit. For the solid at the triple point, we obtain 1.3±0.1 ns, 82±5 ns (Kr) and 1.1±0.1 ns, 18.5±0.5 ns (Xe). Theories on density dependence of lifetimes give only a qualitative description of the exper...
96 citations
TL;DR: In this paper, a computer model for the electron-beam-pumped xenon laser in Ar/Xe mixtures is presented, with the results of a parametric study of power deposition (50 W cm−3 to 100 kW cm−3), gas pressure (0.5 −6 atm), and xenon fraction.
Abstract: The atomic xenon laser operates on seven infrared transitions (1.73–3.51 μm) between the 5d and 6p manifolds. Intrinsic laser power efficiencies exceeding 5% have been previously obtained in Ar/Xe mixtures, principally at 1.73 μm (5d[3/2]1→6p[5/2]2). The kinetic mechanisms responsible for this performance, though, are not well understood. In this paper, we report on a computer model for the electron‐beam‐pumped xenon laser in Ar/Xe mixtures with which we have investigated some of these excitation mechanisms. Based on the results of a parametric study of power deposition (50 W cm−3 to 100 kW cm−3), gas pressure (0.5–6 atm), and xenon fraction, we suggest that the high efficiency obtained in Ar/Xe mixtures is due to rapid collisional cascade to the upper laser level of the 1.73‐μm transition following dissociative recombination of ArXe+ and selective quenching of the lower laser level of the 1.73‐μm transition by collisions with argon. The results of our model indicate that the decrease in laser performance...
92 citations
86 citations
TL;DR: In this article, the electron yields of seven glow-discharge cathode materials under bombardment by neon and argon ions with energies between 1 and 20 keV were measured and the dependence of electron yield on ion velocity was found to be approximately linear for all materials and gases, with the slopes being strongly material dependent.
Abstract: We have measured the electron yields of 7 glow‐discharge cathode materials under bombardment by neon and argon ions with energies between 1 and 20 keV. The surfaces of the samples were conditioned by operating the materials as cold cathodes in a high‐voltage glow discharge before the electron yield measurement. The materials studied are oxidized magnesium, oxidized aluminum, a molybdenum‐aluminum oxide sintered composite, molybdenum, stainless steel, copper, and graphite. The dependence of electron yield on ion velocity was found to be approximately linear for all materials and gases, with the slopes being strongly material dependent. The corresponding glow‐discharge current intensities were observed to have a supralinear dependence on the electron yield. The results are relevant to the design and modeling of cold cathode high‐voltage glow discharges.
83 citations
TL;DR: In this article, the Tl•Ba•Ca•Cu•O high Tc superconductor can be prepared by either two organometallic chemical vapor deposition routes, and the latter is carried out at atmospheric pressure with an argon carrier and water-saturated oxygen reactant, followed by rapid thermal annealing.
Abstract: Films of the Tl‐Ba‐Ca‐Cu‐O high Tc superconductor can be prepared by either of two organometallic chemical vapor deposition routes. Ba‐Ca‐Cu‐O films are first prepared on yttria‐stabilized zirconia using the volatile precursors Ba(heptafluorodimethyloctanedionate)2, Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2. Deposition is carried out at 5 Torr pressure with argon as the carrier gas and water vapor as the reactant gas. Thallium is next incorporated in these films either by vapor diffusion using bulk Tl‐Ba‐Ca‐Cu‐O as the source, or by organometallic chemical vapor deposition using Tl(cyclopentadienide) as the source. The latter deposition is carried out at atmospheric pressure with an argon carrier and water‐saturated oxygen reactant, followed by rapid thermal annealing. Both types of films consist primarily of the TlBa2Ca2Cu3Ox phase, have preferential orientation of the CuO planes parallel to the substrate surface, and exhibit onset of superconductivity at ∼120 K with zero resistance by 100 K.
TL;DR: In this article, the emission characteristics of laser-induced plasma, with the use of a Q-switched ruby laser of 1.5 J, were studied in argon atmosphere at reduced pressure.
Abstract: The emission characteristics of laser-induced plasma, with the use of a Q-switched ruby laser of 1.5 J, were studied in argon atmosphere at reduced pressure. The time- and spatially resolved emission profiles were measured. In argon atmosphere at reduced pressure, the emission period of plasma is elongated to over a hundred microseconds, and the emissive region expands to more than a few tens of millimeters above the sample surface. The emission intensities of atomic lines increase severalfold in an argon atmosphere, in comparison with those obtained in air at the same pressure. Moderate confinement of plasmas and a resultant increase of emission intensities are achieved at 50 Torr. These results are explained by the chemical inertness and the thermal characteristics of the argon atmosphere and the decrease in absorption of the laser pulse by the plasma plume. The re-excitation of emissive species by collisions with metastable argon atoms seems to be less important.
TL;DR: In this paper, the authors used a grant from the San Diego Supercomputer Center, which provided computer time at the CRAY-XMP/48, for a research project.
Abstract: schungsgemeinschaft, the Fonds der Chemischen Industrie, and the Rechenzentrum der Universitat Koln for support. Registry No. He, 7440-59-7; Li', 17341-24-1; Be', 14701-08-7; B', 14594-80-0; c+, 14067-05-1; N+, 14158-23-7; 0+, 14581-93-2; F+, 14701-13-4; Ne', 14782-23-1; BHe2+, 74891-40-0; CHe2+, 53262-54-7; HeN2+. 80896-02-2: He02+. 12269-22-6: HeF2+. 119455-36-6: HeNe2+. Acknowledgment. This research has been Supported by a grant from the San Diego Supercomputer Center, which provided computer time at the CRAY-XMP/48. We thank Dr. Bowen Liu -for helpful discussions. D.C. 'thanks the Deutsche For57143-65-4.
TL;DR: In this article, an argon laser was used to achieve 2.04 mu m in a silica fiber doped with Ho/sup 3+ with an absorbed threshold power of 46 mW.
Abstract: Laser emission at 2.04 mu m has been observed in a silica fibre doped with Ho/sup 3+/. When pumped with an argon laser at 457.9 nm an absorbed threshold power of 46 mW and a slope efficiency of 1.7% were measured.<
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TL;DR: In this article, a special shock tube process combining a reflected expansion wave with a weak shock wave is employed to transfer water vapor carried in argon into a known supersaturated state for a short period of time (0.5 ms).
Abstract: A special shock tube process combining a reflected expansion wave with a weak shock wave is analyzed and calibrated. The process is employed to transfer water vapor carried in argon into a known supersaturated state for a short period of time (0.5 ms). During that period steady state homogeneous nucleation takes place followed by condensational growth. Nucleation and growth rates are measured by a 90° Mie-light scattering technique in the temperature range 200–260 K. The results are compared with existing theoretical models.
TL;DR: In this paper, the authors measured laser parameters for reactor pumping of He/Ar/Xe gas mixtures lasing predominantly at 2.03 μm and Ar/XE mixtures predominantly at 1.73 μm at pump powers of ∼200 W/cm3.
Abstract: We have measured laser parameters for reactor pumping of He/Ar/Xe gas mixtures lasing predominantly at 2.03 μm and Ar/Xe mixtures lasing predominantly at 1.73 μm. Gains as high as ∼3%/cm have been measured in He/Ar/Xe at pump powers of ∼200 W/cm3 . Both systems exhibit small distributed losses. Intrinsic laser energy efficiencies as high as 2.4% (3.0%) have been observed for He/Ar/Xe (Ar/Xe). These efficiencies are the highest reported for reactor‐pumped lasers.
TL;DR: In this paper, the authors measured the partial pressures of the argon and nitrogen gases measured through the target show an apparent drop as power is applied to the titanium target, which is actually a density reduction of the gases in front of the target due to gas rarefaction and heating.
TL;DR: Optically pumped laser action has been achieved over the XeF (B→X) and (C→A) transitions in crystalline argon and conversion efficiencies as high as 30% are observed as discussed by the authors.
TL;DR: In this paper, the addition of a small amount of hydrogen (0.051 min −1 ) in the central channel of an argon inductively coupled plasma was studied and an improvement of the energy transfer from the ring plasma toward the injected species was observed because of the higher thermal conductivity of hydrogen.
TL;DR: In this paper, the effects of gas pressure on the thermal stability of polymer derived SiC fibers were determined through property comparison between the pressure treated fibers and vacuum treated fibers, including properties of the fiber microstructure, weight loss, grain growth, and tensile strength.
Abstract: Commercially available polymer derived SiC fibers were treated at temperatures from 1000 to 2200 C in vacuum and argon gas pressure of 1 and 1360 atm. Effects of gas pressure on the thermal stability of the fibers were determined through property comparison between the pressure treated fibers and vacuum treated fibers. Investigation of the thermal stability included studies of the fiber microstructure, weight loss, grain growth, and tensile strength. The 1360 atm argon gas treatment was found to shift the onset of fiber weight loss from 1200 to above 1500 C. Grain growth and tensile strength degradation were correlated with weight loss and were thus also inhibited by high pressure treatments. Additional heat treatment in 1 atm argon of the fibers initially treated at 1360 atm argon caused further weight loss and tensile strength degradation, thus indicating that high pressure inert gas conditions would be effective only in delaying fiber strength degradation. However, if the high gas pressure could be maintained throughout composite fabrication, then the composites could be processed at higher temperatures.
TL;DR: In this paper, the authors investigated the origin of trapped noble gases in meteorites and found that gases are physically adsorbed on interior surfaces formed by a pore labyrinth within amorphous carbons.
Journal Article•
TL;DR: In this article, high-resolution adsorption with argon and nitrogen at 77 K was performed on large crystals of zeolite ZSM-5 using a novel volumetric device.
Abstract: High resolution adsorption (HRADS) with argon and nitrogen at 77 K were performed on large crystals of zeolite ZSM-5 using a novel volumetric device. Multi-step isotherms for both adsorptives could be observed for the first time. The micropore filling was followed by low temperature microcalorimetry. Exothermic heats of adsorption were found to be correlated with steps in the adsorption isotherms. Based on results from atom-atom potential energy calculations (AAP) as well as from independent model building it is shown that 24 kinetic adsorbate molecules can be situated in a ZSM-5 unit cell. Localized adsorption is presented as possible filling mechanisms. Experimental results are reasonably interpreted assuming primary filling of narrow channels and secondary adsorption in the wider channel intersections. At least for nitrogen there is evidence for a transition of fluid-like to a solid-like adsorbate phase. Compared to argon, Henry's constants and the initial isosteric heat of adsorption indicate a stronger adsorption of nitrogen which is thought to be due to additional interactions of the nitrogen quadrupole moment with the zeolite framework.
TL;DR: In this paper, the enthalpies and velocities of a DC plasma spray torch were measured in an argon confined atmosphere at different currents and argon flow rates.
Abstract: Measurements of local enthalpies and velocities have been performed in plasma jets generated by a DC plasma spray torch, using an enthalpy probe. The torch has been operated in an argon confined atmosphere at different currents and argon flow rates.(1) The validity of the measured enthalpy and velocity profiles has been checked by performing energy flux and mass flux balances, which show reasonable agreement between the input quantities, measured independently, and those obtained by integrating over the experimental profiles. The data are compared with those obtained by operating the same torch in ambient air. The results show that temperatures and velocities measured in pure argon are substantially higher than those in air, and consequently, the jets in argon appear wider and substantially longer.
TL;DR: An electron cyclotron resonance (ECR) plasma stream source at a frequency of 2.45 GHz was explored and utilized for SiO2 film chemical vapor deposition (CVD) as mentioned in this paper.
Abstract: An electron cyclotron resonance (ECR) plasma stream source at a frequency of 2.45 GHz was explored and utilized for SiO2 film chemical vapor deposition (CVD). It was found that for high and uniform plasma stream density the large limiting ring and magnetic fields higher than 930 G are required in the ECR plasma chamber. Plasma densities of(4–6)×1010 cm−3 in nitrogen and (6–8)×1011 cm−3 in argon with uniformities of ±5% over an area of 12 cm in diameter were achieved at distances of 30 to 50 cm from the source limiting ring at a microwave power range of 500 to 600 W. The etch of thermal silicon dioxide and polysilicon with CF4 showed uniformity better than ±1% over 5‐in. wafers at a distance of 19 cm. SiO2 films were deposited in a mixture of 15% SiH4/N2 and O2 at substrate temperatures of 30 to 200 °C. Room‐temperature ECR films had characteristics better than those obtained in conventional plasma enhanced CVD films deposited at 300 °C. ECR films deposited at 200 °C had properties which approach those of ...
TL;DR: Spatial concentration profiles of ground-state SiH and electronically excited SiH* radicals are measured using laser-induced fluorescence and emission spectroscopy, respectively as mentioned in this paper, in pure silane, as well as in mixtures with helium, hydrogen, and argon, in a capacitively coupled glow discharge apparatus used for the deposition of a •Si:H Low power-low-depletion conditions are maintained throughout, whereas pressure is varied from 20 to 400 mTorr.
Abstract: Spatial concentration profiles of ground‐state SiH and electronically excited SiH* radicals are measured using laser‐induced fluorescence and emission spectroscopy, respectively The measurements are made in pure silane, as well as in mixtures with helium, hydrogen, and argon, in a capacitively coupled rf glow‐discharge apparatus used for the deposition of a‐Si:H Low‐power–low‐depletion conditions are maintained throughout, whereas pressure is varied from 20 to 400 mTorr Our observations indicate a close relationship between concentration profiles of the species and local electron energy distribution We conclude that spatial concentration profiles represent stationary generation rates of the radicals In the case of diluted silane the process is strongly influenced by diffusional transport of detected species to the deposition electrode The dependence of this effect on dilution grade and buffer gas used is presented
TL;DR: In this article, in situ temperature measurements of silicon wafers in argon and oxygen plasmas are presented, the processes which determine the heat flow from and to the wafer have been established.
Abstract: In situ temperature measurements of silicon wafers in argon and oxygen plasmas are presented. The processes which determine the heat flow from and to the wafer have been established. It is found that conduction of heat to the electrode does not contribute to the heat loss of the wafer. Radiation of heat and conduction of heat by the gas are the main loss processes. The heat flux qp from the plasma to the wafer is independent of time and temperature. This is attributed to the flux of high‐energy ions to the wafer. By measuring the plasma potential, the energy of the ions is estimated. The ion current density is calculated from qp and the energy of the ions. The value which is obtained is compared to those obtained with other methods. It is concluded that the power density on the electrode can differ by almost an order of magnitude from an estimation using the dissipated rf power and the electrode area.
TL;DR: In this paper, an extensive collisional-radiative model for an argon atom plasma is applied to a low-pressure, hollow-cathode arc discharge and to the positive column of a low pressure glow discharge in order to clarify the mechanisms by which the excited levels in these discharges are populated.
Abstract: For pt.I see ibid., vol.22, p.623 (1989). The extensive collisional-radiative model for an argon atom plasma is applied to a low-pressure, hollow-cathode arc discharge and to the positive column of a low-pressure glow discharge in order to clarify the mechanisms by which the excited levels in these discharges are populated, the results being compared with experimental investigations in the literature. Computations are carried out for various sets of input parameters, such as the electron kinetic temperature Te, the atom temperature Ta, the ion temperature Ti, the electron number density ne, the ground state atom population n1, the plasma column radius R and the escape factors lambda mn and lambda m, characterising the non-equilibrium plasmas under consideration. The predictions of the authors' model. i.e the populations in the excited levels as a function of the electron number density, the effective principal quantum number and the discharge current, are compared with the experimental results and in two cases also with the theoretical results of other authors. It is shown that all calculated dependences are fairly close to the corresponding experimental curves referring to both discharges. The results presented confirm the applicability of the so-called 'analytical top model' of van der Mullen et al. (1978, 1980) and Walsh's formula for Lambda 1n interpreted according to Mills and Hieftje (1984).